Well, I waded into the issue and decided it had to be a lock problem. I found (after a long period of blind scrambling...) that my backup job from the previous night (4 AM) was locking something (Page Lock?) that prevented this query from running. Don't really know why, especially since the command running was a DBCC database integrity check. I killed it, and everything came back to life. Is there a script somewhere that would have found this issue more quickly for me?