They've won against some very good teams. Lost to Lopez/Verdasco, though (in Barcelona). But David having to play on all three days... I'm not sure if that's such a good idea.
It was a stupid decision against Russia, he was totally worn-out against Davydenko and had a strength to play only 1 decent set. But I think that he wants to play again doubles too. If Del Potro steps up like he did last time it is not going to be much of a problem. And on hard indoors surface matches suppose to last less than on clay.