I thought it might be useful to circle around on this one more time with some definitive thoughts. My apologies for the delay on this--a week of intensive BRS training (EMC's new Backup and Recovery Systems business unit formed out of the union of BURA, the previous EMC group to focus on backup, recovery, and archive, and Data Domain) took me away from my blogging.
So where we left things was this: if you want to do image level backups with vSphere 4.0 the present state of the art does not allow an application consistent backup (without the injection of an agent into the guest OS). The underlying reason for this has to do with the present state of VSS support in VMware Tools. Although I am optimistic that VMware will improve their support in the future, and address this issue to the benefit of backup applications like Avamar, at present they only support VSS snaps on Windows 2003 guests (and do not support the extended application VSS writers at all under Windows 2008).
In practical terms, that means we cannot get application consistent backups of Windows applications. However, we can get crash consistent backups. This is actually a pretty important distinction, and I wanted to raise it because I am not sure W. Curtis Preston did enough to describe this distinction in his post on the subject. And crash consistency is a heck of a lot better than corrupted backups (which is what I fear that many people might infer happens if you don't get application consistency).