The Exchange team posted a great piece over on their blog about the reasons
behind going to 64bit for E12. The big doozy here (a 70% reduction in disk I/O)
almost seems impossible but if they pull it off it will more than make up for the
64bit requirement. That type of disk I/O reduction makes running multiple
Exchange 12 virtual machines possible and even probable once we get the windows
hypervisor in Longhorn.
Lot of exciting things happening!