Good overview at The Register. If you're remotely interested in the tech world, you should check them out every day. Good coverage of the most important goings on, with a generous helping of snark.
The Koala - due for its official release today - brings faster boot times, a revamped software installer, better disk encryption, online services, and quite a bit more to the popular Linux desktop.
We took the release candidate for a spin and are happy to report that while work remains, Ubuntu 9.10 has plenty of improvements and that it's well worth upgrading your current system.
Remember, you can make an Ubuntu Live CD, so you can try it out before you make the switch from Windows (or Mac). Kind of a "try before you buy" thing. Except the "buy" is for the low, low cost of free.
Come on - all the Cool Kids are doing it!
UPDATE 4 November 2009 16:55: Maybe you should hold off upgrading for now.