The vibe I get from people is that they're fed up with the GOP at the national level-- but they don't like the Democrats, much, either. This is all theoretical, of course, but I have a feeling that we may see another stab at a viable third party in 2008. So that begs the question:
So far, American third parties have been fringe parties. A studiously moderate third party would be very interesting, indeed, especially as the two major parties of the moment retreat from the center.