Steven,
I am reading your post late, so I hope I'm not going over already
plowed ground. We have had good results using a product named
esXpress to do virtual machine image backups.  For us, the advantages
are that it runs on Linux, not Windows. It is highly customizable.
The output from the backup is an encapsulated script file which you
can move to another server, run the script, and le voila!  Esxpress
is fairly inexpensive, and we have had excellent relations with
company representatives so far. You can see their website at http://
www.esxpress.com/

As a reference point, we have about 24 ESX servers and 318 virtual
machines.

With best wishes,
Keith Arbogast
Indiana University