Running a Debian system that pulls its code from testing? If so, then you recently upgraded from etch to lenny. And if you're still running a 2.4 kernel now some of your servers like MySQL and Postfix will be broken. Postfix threw an error about needing "epoll_create". It seems lenny doesn't work with 2.4 kernels anymore.
Not quite sure why aptitude didn't warn me on upgrade, but the solution is not too hard. Upgrade to kernel 2.6. I did aptitude install linux-image-2.6-k7, said a prayer, and then rebooted the server 2000 miles away. My lucky day, the server came back. There's probably a safer way.
I got some help from the good folks at #debian on the OpenProjects IRC servers. Hanging out there reminded me how lazy I've become as a Unix admin. I used to read kernel patch notes and get excited about libc changes and carefully read docs on every minor upgrade. But that stuff seems boring to me now and Debian generally works well enough that I can just blindly upgrade. Progress of a sort, despite today's hiccough.