I recall the exit polls for Utah were running 90% Romney in the Republican primary among Mormons. When analyzed further, it was clear that many remember what a great job Romney did with the Olympics, they remembered what Hucklebee said about Mormons and his overt bigotry, and they further cited that McCain has never had a following among Mormon Republicans. Romney was really the default candidate because he had done very well when in Utah with the Olympics and he wasn't the other candidates.
Obama did exceptionally well among Mormon Democrats as well, due to his positive speaking ability and because HE AIN'T CLINTON!!!
My personal experience in coming around to support Romney is this. I actually used his religion against him. I know he's an active Mormon and being Mormon myself, I would be branded as supporting him on that basis only. Plus, there were other candidates who had distinguished themselves at the national level already. It wasn't until I began seeing he was gaining the support of the conservative columnists who explained his platforms, his changes in light of what a Republican can and can't do in Massachussets, which I've lived and voted before so I knew what that meant and counted it a plus for Romney, and what he needed to do to attract a wider base than what he had to garner within the Mormon community and Massachussetts. Once I saw he had the mettle and policies that stood apart from his faith, then I came around and supported him as the best candidate in either party.
I hope others did the same thing, even if they didn't get to explain that when polled in the exit polls.