Random June 18th, 2010
When just upgrading this very blog from WordPress 2.9.2 to 3.0 using the automatic upgrade feature the upgrade succeeded at first. Even showing the admin page for that in the new design.
But then, every page either through the frontend or the admin backend simply showed a white blank screen. So it seems when initializing wordpress something goes horrible wrong. As now usful logs where found in the error log of apache it must be something internal.
Reading a nice post in the wordpress forum which refers to the very same problem lead to the conclusion that probably a plugin gone wild. So to resolve this I started to manually move single plugins to a disabled directory in wp-content/plugins. Which revealed wptuner as the plugin causing this issue. To get your blog back online, simply remove the wptuner plugin for now and you will be back in business.
As your blog might use some other plugins that are not compatible yet, your milage my vary here and you may need to disable/remove other plugins too.
Good luck on your journey to a very nice looking WordPress 3.0.