We've released the Exchange 2013 Mailbox Server Role Requirements Calculator.

For more information on this download see: http://aka.ms/E2013Calc

For more information on how to use the calculator, see the above link.  If you have issues with the calculator, email strgcalc AT microsoft DOT com.  Please attach your version of the calculator so that we can diagnose the issue.  I really have nothing else to say here.