The DFS monitoring tool in SCOM 2007 has some great features, which will replace many a custom VB script running in enterprises. As with a lot of Management Packs, to get the most out of it you need to have a dedicated RunAs account with local admin permissions on the servers you are monitoring (e.g. for the Backlogged Files reporting).
The easy (and wrong) option here is to go with the less secure option and distribute a RunAs account to ALL servers.