I finally figured out why Mandrake 9.2 (maybe other versions) slows to a crawl every week. It's particularly bad on a machines with 128 megs, where the data cache is reduced to almost nothing every Sunday morning. A default install creates a weekly cron job with the following command:
nice --adjustment=+19 /usr/bin/slocate -c -u

slocate does not release memory after it finishes updating its db, nearly doubling the amount I'm using from 70 megs to about 120 (NOT including buffers and data cache.) I was rebooting every week to clear the problem, but after deleting the cron job no longer need to.