Some choice quotes:
If you sign any version of a non-compete clause, you will never be a full-time professional writer. Writing will not be your career. Something else will, and you will write on the side for the rest of your life.
I know of at least two mystery writers who need their publisher’s permission to put up a blog post. I know of several more who have had to get a document granting them blanket permission from their fiction publisher to write nonfiction.
Your current publisher might not enforce that clause; the publisher/business your current publisher sells out to might enforce the clause, and make you pay damages for anything you’ve previously published after you signed the contract (and ignored the clause).
Interested yet? Good. Go read it. Seriously, this is important. :/