I just put up a new netapp-qdiff, which is a small script that prints the differences between two quota reports from the same filer taken at different times. (There's a separate program to make quota reports readable.)
The new version has a few minor changes that should let it work for NetApp release 4.x in addition to 5.0, allows you to query a filer directly for the second report (to compare an old report against the current usage), and will also let you query, delay some seconds, and query again (to get information about disk usage changes during the delay period).
It's at URL:http://www.pathname.com/~quinlan/netapp/.
Dan