A week ago or so I fiddled with my mirroring script. To make the fiddling go faster, I commented out the actual calls to debmirror, so I could concentrate on testing the other stuff I was adding.
I forgot to uncomment.
My mirror hasn't updated since.
Moral of the story: when fiddling something, make sure you notice if forgot to re-enable stuff you disable temporarily. In this case, I should've used "echo" instead of ":" to comment things out. Had I done that, cron would've told me nothing was beinge executed.