Here is what Apple says, "Mac OS X performs background maintenance tasks at certain times if the computer is not in sleep mode."
http://docs.info.apple.com/article.html?artnum=107388
Perhaps you should try running the periodic jobs. These jobs are run daily weekly monthly to do general system maintenance. These jobs will clean up the logs.
Macintosh-HD -> Applications -> Utilities -> Terminal
sudo periodic daily weekly monthly
Note: Enter your logon password. You need to be logoned on with an administrator id.
Maybe you should try one of these general clean up programs. You might backup your system before pounding too hard. I'd repair permissions as suggested earlier.
Yasu is a “Universal Binary” Macintosh utility that performs maintenance routines and clears the many cache files used by OS X. Yasu was designed to be a simple, first line of attack for a workstation that has started “acting up.” More often than not, a thorough purge of the cache files of a Mac will bring its behavior back into line.
http://jimmitchell.org/projects/yasu/
OnyX allows you to run misc tasks of system maintenance, to configure certain hidden parameters of the Finder, Dock, Safari, Dashboard, Expose, Disk Utility... to delete cache, to remove a certain number of files and folders that may become cumbersome, to see the detailed info of your configuration, to preview the different logs and CrashReporter reports, and more.
http://www.versiontracker.com/dyn/moreinfo/macosx/20070
