I've been checking the refurb page for months now. Don't worry about a deal disappearing and never coming back if it's a current machine. On the other hand, if you're talking about a machine that's 1 or 2 revisions back, then the chance that it'll pop up later again gets slimmer and slimmer.
A good deal on a refurb iBook IMO is the current 14" iBook. It's $1099, versus $1299 for the regular price and $1199 for Educ. price. Been eyeing that for about a week now. Maybe if my money situation changes soon I'll pick it up.