Rand Paul won the GOP primary in Kentucky, mainly on the strength of extremist tea partiers turning out. Doesn't look like they will have the strength or the turnout to overcome both the Democrats and the mainline Republicans who will more than likely either not turn out for Paul, or who will turn out for the Democrat.
And in the first real test of the 2010 Congressional election, the Democrats were the winners in PA, keeping Murtha's seat that the Tea Party extremists vowed to capture.
The Tea Parties may be strong enough to overturn some incumbent Republicans, but I think, in the long run, that will simply hand those seats over to the Democrats.