I think Thune is a stealth candidate that is better than the "frontrunners" The others, Palin, Romney, etc will flop because they have no substance. He's kinda in a similar position to Brownback last time, in fact Brownback should run in 2012 again instead of as governor, now that "heavyweight" McCain is out of the way.
Thune's drawback that he might be too good looking, perhaps a bit young looking too. He might seem like a GOP version of a 2004 John Edwards, with looks overshadowing substance. But unlike Edwards, Thune actually has the substance, just as long as people get past his looks. In fact, if this were a movie he would be cast as a "perfect" looking president, but real life is far more difficult to navigate on the way to the Presidency.