This particular topic comes up from time to time in discussions. Yes it is OK to run Exchange on VMware, and Exchange 2007 on VMware is a supported configuration… for more info, follow the links below:

The Podcast – Wednesday, Jan 14, for another round of the VMware Communities Roundtable podcast

The Webinar – Jan 15: Exchange 2007 on VMware: Technical Case Study.

The White Paper – Deploying Exchange Server 2007 on VMware Infrastructure: A VMware Internal Case Study

The original post from VMware

Timely blog posts for the WIN! This came up at the office today, that is to say, is running Exchange in a VM a good idea? The general consensus was that "YES” it is. You see those quotes there, they’re significant. That is not to blanketly say that running a massive Exchange deployment in a VM (or VM’s) is ok. There will need to be some intelligent design and engineering around this, but it is entirely possible, and if done right, can outperform your physical deployment.

That said, Mike Laverick at RTFM-Ed posted some examples today that YES it can be, and is being done.