I recommend anyone who is considering virtualizing MS Exchange read Jim Lucey's blog post and the comments below his post. VMware's HA guidance on virtualizing Exchange could be mis-interpreted, resulting in increased storage costs and placing data at risk.
Here's an excerpt:
We love that our customers are excited to deploy Exchange Server within virtualized environments. While VMware leveraged Exchange performance and sizing tools to provide guidance, their recommendations casually tiptoe around Microsoft system requirements, unnecessarily increasing storage and maintenance costs and putting customers at risk. Exchange Server 2010 provides choice and flexibility in deployment options. We are committed to virtualization technology deeply, and will continuously review as the various technologies evolve. We hope to do even more in the future with our roadmap. As we work to test and update guidance pertaining to Exchange running under virtualized environments, our current system requirements are in place to give customers the most reliable email infrastructure possible.