There reportedly seems to be some kind of agreement that no release should occur 2 weeks before the official string freeze. That occurred very recently. There are still 20-30 tickets in the WP 2.9 todo list. So it’s mostly nit picking at this stage.
Some neat features make it definitely worth the upgrade. I wouldn’t jump on 2.9.0, however; especially if you’re using plugins that aren’t as well maintained as those from Semiologic Pro. There are over 1,000 tickets in total at the time of writing this post, and WP 2.9 introduces some subtle changes in the schema that may break a plugin here and there.
In order to deal with the WP upgrade, I’ll be releasing an updated Version Checker in the next couple of days. It’ll disable the WP upgrade nagging until WP 2.9.1 is released. (The same for 3.0, 3.1, etc.)
In other news, Semiologic Cache 2.0, which I’ve yet to start using on this site, but which I’ve been working on all week, is starting to look very cool. More on this in a later post.