At the last Wedding Walk, I was talking to a Sony Alpha user that was on the verge of jumping the fence to either Canon or Nikon for one reason alone. He was about to start shooting weddings, and Sony did not have a full frame camera option. At least one with newer technology that has already been surpassed by Nikon and Canon by a whole bunch. The last camera from Sony with a full frame sensor was the A850, released back in 2009.
Shooting weddings with a full frame sensor camera, means you are likely to also get stellar ISO performance as well. And for those that want to write in saying that there are plenty of cameras without a full frame sensor that can shoot a wedding competently, I would only say that experienced photographers will tell you that they like a full frame better for a host of reasons that I won't go into here. Can a cropped sensor camera do a great job? Sure. But if given the choice, experienced hands that have shot both will go to a full frame almost every time.
Well, Mr. MC Neal from the Wedding Walk, this may change your mind on jumping ship. We have a leaked spec list for the new Sony A99, and it looks pretty good. Asking price is rumored to be about $2,800.