Today I found a system message on my Apple laptop: "Your startup disk is full!". Scary! Who ate 45G space of my main disk just per one night?!!
Guilty was a huge error log[s], which was generated in /Library/Logs/Console/... because I've downloaded a XVid plugin for QuickTime: http://n.ethz.ch/student/naegelic/index.php for playing with, but this beast didn't throw any complains, just silently generated huge amount of rubbish data.
Also one interesting moment: after I had removed the logs (rm command) and sync'ed disk, space still didn't changed at all. Everything fine become only after complete machine reboot. Weird.