The iOS 6.1 update, released 1/28/13, introduced a new bug with iOS devices connecting to Exchange servers. If the user replies to a recurring Exchange calendar event, the iOS device can begin generating excessive amount of traffic to the Exchange server. This increases the CPU utilization on the Exchange server, and causes the iOS device to run slow and experience reduced battery life.
Apple has released the iOS 6.1.2 update on 2/19/13 to correct this issue. It is highly recommended for all iOS devices connected to an Exchange server running iOS 6.1.