The Microsoft Exchange Team released an update of the Exchange 2010 Mailbox Server Role Requirements Calculator. The new version is 3.5 and it includes the following features/improvements since 3.2:
Improved the text on the input tab with regards to the number of database copy instances you would like for both HA and lagged copies. Also fixes an issue where in a high availability architecture the calculator may size the solution based on activating more database copies during a second server failure event than the total number of database copies deployed on the server.
Corrects a memory and CPU utilization issue where you deploy a site resilient architecture with multiple mailbox servers and a single database copy in the primary datacenter. Specifically, the calculator would determine the active database copy configuration after a single server failure and then size the CPU and memory requirements. However, since there is only a single database copy in the primary datacenter, the solution cannot survive with all copies hosted in the primary datacenter. Therefore, the copies need to be activated in the secondary datacenter. Version 3.4 corrects this scenario by ensuring there are at least 2 database copies in the primary datacenter in order to calculate the active database count after a single server failure.
You can download the calculator here.