The Exchange 2010 Mailbox Role Requirements Calculator has been updated again, the latest version being 4.5. I would urge all readers to keep an eye on this space, as new versions will be uploaded. The latest version has included new options like considering whether you have a 32 or 64bit GC in the environment. The calculator only supports active/passive environment even now.
Download v4.5 here and read the explanation of all the options here
