I have two different customers experiencing the same problem today. Windows 2008 Server virtual machines running exchange 2007. The servers are extremely sluggish and non-responsive. If you reboot the server it functions normally for about 4 minutes before it begins to get sluggish again. Nothing in the events logs is noteworthy. Other servers on the same vmware host and san are running fine.
The last set of windows server patches were applied last week.