I think the general consensus here is don't use it for production or you're asking for trouble. The biggest downside is you have to spend money for a SQL server license to use VirtualCenter. See this thread also...
http://www.vmware.com/community/thread.jspa?threadID=67175
Page 57 of the install guide says "MSDE is not supported for production environments. You must use an Oracle or SQL
database to receive enterprise support."
So if you have a problem and have to call support they might not help you with it if it is database related.
http://www.vmware.com/pdf/vi3_installation_guide.pdf