I'm a bit conflicted here. I can't stand the black-and-white, no nuance, flip-flopping political world we seem to have reached, in which a politician is not allowed to change their mind on an issue. On the other hand (the flip side, if you will), the timing of Romney's change of heart is awfully politically expedient, corresponding as it does with his move away from liberal Massachusetts politics onto the national stage.
I guess we need to look at them on a case-by-case basis. I don't believe that Romney has convictions on abortion one way or the other, though I'm willing to believe at this point that he'll do whatever it takes to earn the support of social conservatives. And from where I stand, it doesn't matter whether he seeks to outlaw abortion because he is morally opposed to it or because it is politically convenient: either way, it's a giant reason for me to dislike him and his candidacy.
The other big flip-flop issue in this campaign is Clinton's vote on the Iraq War. Obama won't let anyone forget that he was against the war for the start (as was Kucinich), but the other Democrats authorized the war. This, too, is a politically expedient position by Clinton. The climate when the war was authorized was such that votes against it were easily branded as votes against safety. A politician who wanted a legitimate shot at the White House couldn't afford--back then--to vote against the war. Today, to win the primary, it is politically expedient to be against the war, and so she is. I do appreciate the nuance in her positions, however, acknowledging the logistic difficulties of an immediate, full-scale withdrawal from Iraq.
So in the end, I expect my political leaders to be intelligent. And I expect intelligent people to change their minds, within reason. So I don't lend much credence to attacks on flip-flopping. Instead, I look at a candidate's current view and evaluate that. And if someone lies, they don't get a second chance.
(As an aside: attempting to discredit the abortion-related attacks because the group is a "gay rights group" and Romney is proud to not support gay rights is both illogical and offensive at the same time. Good going there, spokesman Kevin Madden.)