Many commentators seem to believe that the Tea Party represents a net minus for the GOP because of the split between them and the existing establishment. This criticism seems oddly familiar to me. Many people predicted that the drawn out fight between Hillary and Obama would be the death of the Democrats in 2008. As it turned out, that extended fight kept them in the news for months and built up the ground networks that helped Obama carry the day in states that normally be out of reach for a Democrat. Take Indiana, where Obama carried the state by ~28k votes. Does that happen without the ground operation built for the primary and the name recognition/publicity gained from it? Impossible to say, but I think it's clear that the intra-party squabbling was a net positive for the Democrats in the end.
It seems likely to me that the Tea Party will have the same impact on the GOP. They may well prove to be a net minus in selected races (Delaware) but the enthusiasm they've generated and the new people they've brought into the political process will more than balance that out come November.