The savings from deleting log files is likely negligible. Instead, you should look at other threads that explain how to remove unnecessary printer drivers, language files (search 'Monolingual'), and PPC binaries (search XSlimmer).
BTW, the largest hidden file is the 2GB "sleep file" which you can free up by turning off "safe sleep." If you really want to know where your space is going, check out the great freeware app "GrandPerspective."