Well, I was a little bit off with Federer, I didn't expect him to go out in the third round to Stanislas Wawrinka, but it's hard to make predictions for Federer now a days because he's so erratic. Anyway, these are my predictions for the semi-finals:
Nadal vs Murray:
Nadal, kind of obvious, he's much better on clay than Murray. I don't think that this will be close at all. Nadal in straights.
Djokovic vs Wawrinka:
A few days ago Stan won his match against Roger Federer but I would be surprised if he was able to upset Djokovic. The Djoker has a big lead in their head to head and has beaten Wawrinka on clay. I think Djokovic moves through in two very tight sets.