I just stumbled across something which I thought might be more than helpful to a few of us. VMware has a documented issue when upgrading vSphere 4.0 when the HP Insight Manager agents are installed on the host. The short version is that the Insight Manager services must be disabled before attempting to upgrade the host, or the host can be left in an unstable partially upgraded state.

The full article can be found here: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1016070