Directory size tracker for file server.

I have always wanted to be able to easily track the size of each directory on my file server. That way, if its free space drops by a gig in one day, I can see what directory caused that and talk to the owner of that directory. I found a shareware program at http://www.filesuniverse.com/ called Space Searcher and it looks like the answer to my problem but I thought I would see if anyone here knows any pros or cons of that software or knows of a better software for my needs.