I wonder -- in case something like this happens again (or even in cases of Severe Just Nothing Happening) -- if there's a way to have the servers notice "Hey, we've been pretty dang idle for about five minutes. Maybe we could do some expensive internal stuff that doesn't really involve a lot of mail." Something like an expunge-very-old-deleted-users run? (Though I think you tend to give a courtesy heads-up in a news update before those get run, often...)

I'm thinking an internal activity monitor that notices when load dips below a certain threshold for a certain length of time, and then starts doing some queued crunching that might have otherwise been saved for a maintenance window?