I just ran accross something interesting, it appears that Microsoft have a command line tool specificly designed to test the newer VSS based backup interface of Exchange 2007. It is not overly pretty but it does appear to have both a backup and restore option and as the benchmark of whether the behind the scenes backup stuff is working should be robust.

The tool is described here:
BETest Tool (Windows)
and sourced from inside here:
Download details: Windows SDK for Windows Server 2008 and .NET Framework version 3.5

The procedure is described here in the last section (The BETest Tool):
Exchange 2007 Data Backup and Volume Shadow Copy Services

Probably a false alarm and crippled in some way but may be worth a look at some point for someone with an exchange 2k8 testing environment to play with.