Finally wordpress has revisions on posts.
Which makes it a lot easier to share writing between people -- since you can save your copy, and the other person can see what you changed.
Also you can revert to previous revisions of posts you've made.
Theme preview, so you can try out themes before others.
But most importantly they have made images easier to use. 2.5 was seriously 'special' when it came to uploading images. A lot of people couldn't upload images in 2.5 because of they way the interface was not-designed.
It also has partial support for google gears (to serve some parts from a local cache). Which apparently speeds up loading the admin section.
Full details of wordpress 2.6 release.
ps. Also pygame 1.8.1 release candidate 2 was released, with 1.8.1 release planned for this weekend.