As I was recently running low on disk space, I began looking for files that used a lot of disk space on my hard drive. I didn't remember activating the crash reporter in /etc/hostconfig (see this hint), but it was enabled. When I looked at the crash reporter log file, /var/log/crashreporter.log, I discovered it was up to 8GB! Give it a look if you think you are losing some disk space for no reason...
[robg adds: I think crash reporter was enabled by default in some recent release of OS X -- 10.3, perhaps. I know it's enabled by default in 10.4, as my two clean-install machines have the CRASHREPORTER=-YES- line in their hostconfig files. I'm not sure what it would take to create an 8GB crash reporter file; on both my machines, the file is under a few KB in size.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050727122644858