I know I'm a little late to this game, but I have a suggestion that we are running here...
It's great... runs on Windows, Unix and Linux and it's even GPL'd.
http://www.tucows.com/preview/51638 Set it up to monitor the directories of concern, run it a few weeks, while you put in exceptions for particular files that you don't really care about, and you're set. We have it monitoring our core Unix system as well as the Lawson system.