One issue which wasn't raised other than in passing, though, is that there are two distinct types of series, and the kind of support work one does for each is going to be different.
Most of the writers on the panel had or were working on single-story series, the kind where there's some single story arc which the series as a whole is focused on resolving. The classic example here is of course Lord of the Rings, which Tolkien never considered to be a trilogy, IIRC; it was written as a single novel, and was published in six "books" organizationally, and in three volumes because, well, page count. But there are plenty of other series nowadays where there's a single story and you really do have to read the whole thing, in order, to get the entirety of this single story. No skipping, no reading out of order, and if the writer dies in the middle, the whole thing up to that point (both the writing and the reading thereof) has been pretty much wasted because you're never going to get the entire story. Someone (it might've been Seanan, actually [squint/cogitate]) asked whether it wasn't a lot easier to keep people coming back and reading if each book of the series wasn't an actual ending, but just the close of the current act. That might be true for some people, I suppose. It'd be interesting to see some good survey data on that. [Scribbles a note for an RTB column.]
The other kind of series, though, is the true episodic series, where each book is self-contained and when you come to the end, you have the entirety of that particular story. There might be some farther-reaching plot points which color all or many future books, and there might be character development which likewise shows in future books, but you generally can pick up Book Six first and read it and understand who's who and what's going on. You might feel a bit of confusion if some character or event from a previous book is mentioned, but it won't be a key point in the current book (or if it is, it'll be explained) and you'll generally get almost as much enjoyment out of the book that someone who'd read the whole series up to that point would've gotten. A good example of this which comes to mind is Mercedes Lackey's Diana Tregarde series. Each book or short story is stand-alone. There's a chronology, and there are mentions of people and events from earlier in Diana's life in the later stories, but you can pick up any story and get what's going on, and there's no point where being unable to read the next one would make you want to smash something.
The clear advantage of this second type, of course, is that if the writer gets hit by a bus at some point, it'd be a very sad thing but at least the readers aren't left hanging with three-quarters of a story and no clue what was going to happen or how all these dangling plot points and perilous obstacles were going to resolve. And likewise, if a writer just loses that particular muse, or starts chasing a newer and shinier muse, or if the publisher decides they don't like the numbers from Book Six and therefore declines to contract for the projected books Seven through Twelve, it's a disappointment to the readers, yes, but it doesn't leave this ragged, bleeding hole in the series.
A major disadvantage of the first type, or at least the one which annoys me the most personally as a reader, is that if the story is complex enough, you pretty much (or I do -- maybe it's just the way my brain is wired) have to read all the books bam-bam-bam, because in the year or more which passes between books, you forget who's who and what's going on and what the characters were planning to do about this problem here, and cetera. Harry Turtledove's Worldwar books had that problem for me -- I read the first one, then a year later I got the second one and had no clue what was going on. So I reread the first one, then read the second one. A year later I got the third one, couldn't remember the characters or what each person/group had been doing again, so reread the first and second books, then read the third one. Then the fourth book came out and I couldn't remember.... [headdesk] These books are like two inches thick, so rereading all the previous ones every time a new one comes out is no small undertaking. As time went on, it was more and more difficult to find a large enough chunk of spare time to sit down with the whole stack and catch up before reading the new one. When book four came out, I never did read it, although I bought it. There are three or four more books after that too (technically a different series, but the same verse and chronology, so I look at them as the same series) and although we might actually have those around the house somewhere, I haven't read them and might never. I really love Harry's work, and have since Guns of the South, but jeez.... :/
Part of the problem here is that these books are complex, with multiple protags, each with his own goal, own plotline and own set of supporting characters, and for the most part each protag's storyline takes place in some chunk of the world (or up on the invading alien fleet ships) distinct from the others. (Very similar in structure to most of the Niven/Pournelle collaborations, like Lucifer's Hammer, for folks more into the harder SF.) So it's not just a matter of remembering who the protag was and what he was doing -- you have to remember all the protags, all the storylines, and which goes with which. I have a mind like a steel sieve when it comes to fiddly little individual data items and couldn't do that. I'll admit I don't have quite such a hard time retaining info about single-plotline series if there's really a single plotline, with a single protag and only one actual story to keep track of. I enjoy the more complex, braided-plotline books, but when they're series I just can't keep track of all the different names and events and info from one year to the next.
And of course, there are going to be distinct differences in the prepping and writing for each kind of series. With a single-plotline series, you need to keep track of the over-all storyline, where the volume you're writing right now fits into it, which threads from the previous book(s) you're picking up and furthering in this volume and where you have to lay threads which will be picked up a volume or three later, making sure your greater, series-long plotline progresses just enough and in the right way. At the same time, you need to do all the usual novel-plotting for the current book. (I'm assuming most writers would want to at least kinda-sorta pretend that each volume is a story with a beginning, a middle and an end, despite evidence to the contrary in my own reading [cough] and that there will actually be a smaller plot arc over the course of the current volume. In a way it's just more of the same thing you do for a chapter or a cluster of chapters for every novel, but that difference of scale is a pretty significant one.
Whereas with a more episodic series, you need to keep track of your bible, make sure you're consistent with all the usual setting and character things from one book to the next, and maybe track one or two threads of a larger event or of character development which run between books. Most of the plotting, though, will be complete within the volume and won't have to fit perfectly into its place as Act Five of an eight-act plot, or anything like that.
There are, of course, advantages and disadvantages to both kinds of series. I just thought it was interesting that the second type was pretty much ignored at the panel. It makes me wonder whether it's a blip in the SF/F genre, or among this particular group of writers, or whether it's a more general trend in commercial fiction. If it's actually the general-trend thing, it hasn't hit my end of the business, for which I am profoundly grateful; there are plenty of episodic series which do very well indeed here, and I'm working on a couple myself -- one urban fantasy and the other SF. I know Sean Michael, one of Torquere's most popular writers, has a very successful series about a private club (which I think is a space station but don't quote me) called the Velvet Glove, which is episodic. And Laney Cairo's Liminus Australis series, set in a future Australia at war, isn't going to be completely episodic, but there aren't any ragged, bleeding plot threads left at the end of Running the Nullarbor, which is the first book. Aaand... [squint/cogitate] I'm willing to accept that there are probably some multi-volume stories too, although I can't think of any right now. [duck] So the market's definitely there for the full range of series types, and I'll be keeping several sets of virtual fingers crossed in hopes that the situation will remain stable for at least the next few years.
There was also some discussion of protecting your drafts and notes, and a story about how one person's 700+ pages of series notes vanished with a blown hard drive. Ouch. :/ At any given time, the entire contents of my STORIES folder is on my main computer, my laptop and a flash drive. The laptop and flashdrive aren't always completely up to date (probably not as often as they should be) but at least my chances of losing everything are pretty slim.
Someone mentioned completely off-site backups, which are a good idea. There are various ways of doing this, but despite some skepticism from one or two people attending the panel, I think GMail works dandy for this sort of thing. Not as one's only backup option, of course, but if you've got other backups too, the chances of everything going blooey all at once become remote.
Wikis were mentioned for organization, and I'll admit I've thought about this too. Right now I don't have enough info on any one series to make the work of setting up a wiki in the first place cost-effective, but it's something to keep in mind as the bulk of data and frequency of look-ups grow. I know a couple of writers personally who have wikis for their writing and they seem to work well. It's just the initial time investment, and then the required obsessiveness to keep everything updated and linked and all; I'd rather save that kind of effort for when I have more than three or four stories in a series. For right now, my notes files are working just dandy.
Oh, and there was some discussion of pitching your series differently depending on how many books the publisher will be willing to buy. So for example, you'd want to be ready to pitch a stand-alone book, a two-book series, a trilogy, a five-book series, etc., explaining how you'll