According to a bug report from Microsoft, when an iOS 6.1 user syncs a mailbox, the "Microsoft Exchange Server 2010 Client Access server and Mailbox server resources are consumed, log growth becomes excessive, memory and CPU use may increase significantly, and server performance is affected."
Microsoft has given Exchange admins some workaround methods to keep things running smoothly while a fix is underway. I'm sure this is inconvenient for both companies as well as consumers, but Microsoft getting to tell its users not to use iOS products? What a convenient inconvenience.
via The Verge