Philip Klein thinks the flip-flopper charge will be more problematic for Romney in the general election:
During a primary, there’s a certain political balancing act to flip-flopping. On the one hand, changing positions makes a candidate seem inauthentic, but on the other hand, people like it when you agree with them. … But should he be become the nominee, Romney will have to earn the votes of a lot of people who don’t necessarily agree with him. So he’ll essentially get all of the political downside of being a flip-flopper with none of the offsetting benefits. On top of this, he'll have less leeway to shift positions during the general election than typical nominees, because even the slightest change would reinforce the charge.