I didn't see anything about this specific issue and it strikes me as a weird one. On our WPMU 2.8.6 and now on our WPMS 3.0 installation I occasionally encounter a blog that white screens for no apparent reason. The blog was fine one day and then it is white screen the next and white screen when trying to get to wp-admin (even for Super Admin). This is probably a PHP error, but why would it work fine and stop? Here is the most recent example http://historyofslavery2010.voices.wooster.edu/ I don't have permission on the schools server to be able to ge the logs. I'll get those next Monday when the sysadmin gets back. Hopefully someone can decode them at that time, unless anyone has thoughts now.
This does raise some other questions for me? Is there a plugin that will allow the Super Admin to see which blogs are using specific plugins? This would be great for dropping ones nobody is using. Also, if it is a plugin is there a way to diable all the plugins for a specific blog even when you can't get to wp-admin?