Apparently, versions of Mac OS X before Tiger used to write Console logs to a directory named for your short user name:
/Library/Logs/Console/shortu/
i.e. shortu is the user's short name. Apparently in Tiger, console logs are written to a directory named for your user ID number instead:
/Library/Logs/Console/501/
However, Tiger does not delete the old console logs or directories, even though they are no longer being used. So if you updated to Tiger from a previous version of Mac OS X, you can save some hard drive space by deleting the /Library -> Logs -> Console -> shortusername directories for all of your users. Don't believe me? Try typing this in the terminal:
head -1 /Library/Logs/Console/501/console.log
The 501 user ID is assigned to the first account that was set up by the OS, and "newer" users are numbered higher: 502, 503, 504, etc. After that, try this:
head -1 /Library/Logs/Console/your_shortusername/console.log
These commands will tell you which OS versions wrote each file.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050930123027552