It's on your end. Your theme, your plug-ins, or your install of WordPress somehow got messed up and you need to re-upload 2.8.
I have 4 seperate blogs of my own, and have admin access to 5 more.
I updated all 9 with WP 2.8, and they all run great.
All have plenty of plug-ins and some have complex themes.
I didn't have one single problem with all 9 when I upgraded to 2.8.
Well, I take that back, I forgot to rename the default theme after I edited it on one blog, and it go overwritten back to the basic default theme, so I had to re-do it. My mistake completely.