Ok, so thanks to Colin, I was able to get a preview of Wordpress 2.5 (username:admin password:demo).
First impressions: Looks cool, I can see how they made the menu a bit easier, and make more sense. You now have “Write – Manage – Design – Comments”. Off to the right, you have “Settings – Plugins – Users”. So already, the important stuff is glaring out at you on the left side, and the semi-important things are in smaller text to the right. 
Not much has changed functional wise that I can tell, and I’m pretty sure that’s been stressed before, except for the looks in the dashboard. I certainly hope the plugin developers get a preview version of 2.5 so they can plan accordingly. Although I believe wordpress has it covered in the Migrating Plugins and Themes page. It’s really different!
On the write page, I’m not particularly keen on having the categories go underneath the entry. I do like how they have made it easier to tell the status and time of the post, however, I liked the categories just where they were. I’m also betting because it’s still Alpha that the “sections” will still be movable just like it is now. i.e. you can click and drag the order of the boxes on the right. I really like that option. Then I can move what’s important to me where I want it.
I do, however love the layout for the new widgets. And they do compensate for multiple sidebars very well. I’m using 4 sidebars on this site, so it gets kinda wacky because of the page position and such. Sometimes I have to drag things to one bar to get to another. The new system is much better. I like that.
All in all, I’m highly anticipating it. I just hope the plugin developers will be able to keep up. I’ve got enough plugins to where I won’t be able to upgrade very easily.
I don’t like it. It’s got orange. I like my WordPress like I like my women (random Eddie Izzard reference), blue! Sorry it’s late and I’m tired.
Generally it’s looking very web 2.0 complete with large fonts and oversized field boxes but I don’t like that they’ve moved everything around so much! I like the way things are right now a lot. Oh well, I could just be moaning for nothing and end up realising that these changes are all for the good. I will agree with you on the positioning of the Categories though. That has to be movable to the side.
I like WP, but it seems like whenever I upgrade, a new version comes out a few days later. Drives me nuts.