WordPress 2.8 Baker is now available as a full release. 2.8 has a whole bunch of bug fixes, has improvements to themes and widgets and has added some fantastic taxonomy features. The WordPress dev blog post linked above goes into detail about what is new. Users are now able to browse the WordPress theme directory and add themes with one click. 2.8 should also be faster to use overall.
I don’t see my upgrade bar yet but since the final version bump just went in, the upgrade notice should be there soon. You can read a review of WordPress 2.8 we did earlier. If you already know about and were eager to upgrade, you can download WordPress 2.8 or use the automatic upgrade option to upgrade to it.