For a long time the answer was no, but developments in the VMware Products have lead to major improvements in disk/network/memory and CPU performance so now the question is…
Where do I start ?
If your looking for a good starting point I would listen to the recent podcast from the VMware community round table which was specifically on virtualising Exchange..
Also you may want to check out the VMware pages written especially for virtualising Exchange, make sure you check out the resources tab….
It would seam that after years of advising against it even Microsoft are jumping on the band waggon:
With the release of Microsoft Windows Server 2008 with Hyper-V and Microsoft Hyper-V Server 2008, a virtualized Exchange 2007 SP1 server is no longer restricted to the realm of the lab; it can be deployed in a production environment and receive full support from Microsoft.
Check out the full article on the Microsoft Exchange Team Blog here