Stratford Conservative has written a blogpost questioning whether this poster has backfired on the Conservatives. He thinks not. I tend to agree. Any poster which is still being talked about two weeks after it first appeared has to have something going for it. Cameron dealt with the airbrushing issue with good humour and I think the fact that it has generated 74,000 new versions rather speaks for itself.
I think my only question about the poster is why did every poster say the same thing? OK, you get uniformity of message, but if there had been five or six slogans I don't think the main message would have been diluted. But then again, what do I know?