On Cristiano's weblog there's a great write-up that shows you how to extend the MOF file in an ESD system like SMS that will allow you to see what is on the client for virtual applications. 

I haven't tried this myself and since it's not an official Microsoft tool there are no warranties or guarantee's.  This is one of those 'use at your own risk' type of things but it looks pretty slick.  Check it out here.

- J.C. Hornbeck