I don’t think the ad is going to backfire. I think it was the intent of the Log Cabin Republicans to pay for the ad in order to decrease support for Romney; and it will work. The only probem for the Log Cabin Republicans is that those awayed by the ad are not going to go to Guiliani. They will mostly go to Thompson and some, to others.
The statement from Romney's camp also points out that the Log Cabin Republicans are playing favorites for his opponent, Mayor Rudy Giuliani (or I guess it could be McCain or Fred since they don't support the Federal Marriage Amendment either):
“This personal, negative attack was launched and paid for by a group recognized as having Mayor Giuliani as their ‘favorite’ candidate," Madden said. "Governor Romney supports a federal marriage amendment and so it makes sense that a national gay rights group would attack him. The advertisement misrepresents Governor Romney’s courage to admit that he had been wrong on this issue and the fact that he is proud of his strong record of defending the sanctity of life.”
The gay Republicans attack against Romney could turn out to be a positive for the candidate, according to speculation by some political pundits. A New York Times blog post by Jim Rutenerg theorized that "even those conservatives who will buy into the flip-flop claim may take heart that he has 'flip flopped' to their way of seeing things."