Performance was severely degraded for a couple hours. We tried a bunch of things, none of which worked, and then I suddenly remembered that I had pushed a trivial code change just before things went to shit. Reverting it made the problem go away. Doh! I still don't understand why.<p>Sorry everybody!<p>Edit: it was not for naught, though, because some of the tweaks that the incredible mthurman came up with seem to have made things a bit snappier than they were before.