Well I am slowly upgrading all of my sites to WordPress 2.8 and damn it seems good. One big site that I have was having trouble though. I was getting 500 internal server error after doing an upgrade on a rather large blog and this is what I now do to troubleshoot all WordPress errors.
1. Rename the /wp-content/plugins folder to plugins2 this will disable all plugins since the system will not find them
2. If this works and my blog works (It was kinda better but still slow and partially broke) then you can copy that folder to a drive on your machine and then delete all the plugins in that plugins2 folder, delete all the plugins, rename the folder back to plugins, and then add one at a time and see if everything is good. This can help you troubleshoot a bad or memory intensive plugin.
3. Inm my case I found that the blog was still sluggish so I used that hack for getting PHP 5 to work on 1 and 1 internet. I added AddType x-mapp-php5 .php as a line in my .htaccess and this fixed the 500 internal server errors.
Does this work for you? Do you like the new WordPress? Here are the main new features:
That is a crapload of change. The interface though is very similar to 2.7 though which is nice. There are also apparently 100s of bug fixes as well and everyhting just feels more stable.