This thread is discouraging to me...
I upgraded to 2.8 last month, using the auto-upgrade plug-in. At first, everything was fine. Then the visual editor stopped working. That was annoying, but today my dashboard broke. What I see on wp-admin looks remarkably like http://metalseinen.com/PubImages/4-1.JPG
The gradual degradation of WordPress is the strangest part of this. I haven't tried to do anything fancy with WordPress since I installed 2.8 -- I just use the program (to add the occasional post, read my comments, and review my spam). Probably the fanciest thing I've done was to add a couple of additional spam-words to the moderation list.
To address this, I've disabled all plugins except Akismet, but that hasn't helped any. (Other than Akismet, I was only running the backup plugin and the auto-upgrade plugin. I don't want to lose Akismet, as I'm getting a lot of spam these days, which Akismet is effectively blocking.) I started to replace WP files, but the network administrator on the system I was using blocked my FTP access before I could finish the job.
Here's hoping that replacing the wp-admin and wp-includes directories does the trick!