(moved over from feedback forum)
A few things to look at for 2.6:
1. Support for widescreen (or maybe just high resolution) monitors. I have my resolution pumped up to 16x10 and when I write a post/page, editor only takes up half the screen instead of stretching across.
2. Plugins section. It was convenient to know which ones were outdated all at once and at a glance on the previous version of WP. Currently, you have to look at each plugin individually.
3. Retroactive changes to pictures. If I post pictures using the gallery feature (which I like, btw), and then decide I want to change the default thumbnail size in options, I have to repost the pictures in order for the changes to take effect. Of course, I might be doing something wrong, so you tell me.
Overall, awesome upgrades. Keep up the good work.