I had this problem and, through my inept tinkering, ended up actually completely destroying both of my new 2.8 blogs. Turned out it was a php memory limit set by the service provider and NOT customizable by me. The 8 MB limit my provider gives is not enough to run WP 2.8.
I was running only ONE plug-in (Akismet), and I had small databases (less than 2 MB each) but I still couldn't run WP 2.8 on account.
I think this is a major bug that the WP development community needs to fix. I want to use WP... it is clearly the best... but at present I just can't do it. Also, after porting over to my self-installed WP blog, I deleted my old blogger blog, and after this fiasco, all that I have left is the MySQL database. My old blog is now totally off line.
I'm feeling kinda bitter about this issue.