Marc Ambinder writes in National Journal about the "evolution" of Mitt Romney's views on the key social issues of same-sex marriage, abortion, and stem-cell research. Ambinder, who runs National Journal's Hotline blog, has historically not been Romney-friendly (example here) but the article seems thorough enough.
To this observer (a committed Romney supporter) this whole discussion seems to miss the point: What will Romney do as president? It would be very difficult for him, after the very public, controversial positions he has taken on those issues, to back away from those positions as president.
If you believe him when he says his views have changed, then there is no reason to be concerned. If you don't believe him, and nothing he or his supporters say can change your mind, then by all means, support Brownback or Huckabee, and be ready to see John McCain as the nominee.