Apple has just released iOS 6.1.2, their second minor point update, and as promised it fixes a bug that's caused network activity problems for Exchange calendar users.
iOS 6.1 was released on January 28 with Siri movie ticket purchases in the U.S., and increased LTE support internationally. iOS 6.1.1 was released on February 11, but was exclusive to the iPhone 4S, and fixed 3G network connectivity problems.
A separate iOS 6.1.1 beta was released to developers on February 6, mostly focused on Maps improvements for Japan. That update is still awaiting release will likely be re-numbered.
If you've been experiencing the Exchange calendar issue, let me know how the update works for you.