Today we've released an update to the Exchange Server 2010 Mailbox Server Role Requirements Calculator that addresses some issues that were identified in the previous (v12.8) release. You can visit the updates tracking page to see what is in this new version, but here’s a brief synopsis of what’s fixed/changed:
You can find more information and download the calculator on the Exchange Team blog at http://msexchangeteam.com/archive/2009/11/09/453117.aspx.