How Important Are Gaffes?

Brendan Nyhan puts Obama's "private sector is doing fine" gaffe in perspective:

Negative ads are indeed the most likely way that Republicans might try to make the quote salient in the fall. The problem, however, is that evidence for the effectiveness of negative ads is quite limited. The best experimental evidence suggests that the effects of television advertising decay quickly. Moreover, as Georgetown University political scientist Jonathan Ladd pointed out on Twitter, the relevant question is whether ads (or speeches or commentary) that exploit gaffes are more persuasive than the material Republicans would otherwise have used. How much will it matter if a Romney ad quotes the "doing fine" statement or, say, criticizes the stimulus or healthcare reform instead?