Since the climb is long and gradual, but 'not too steep' (only 6.9) I think Basso, Menchov are the favoured climbers today. The steeper sections are early on in the climb as well, which might be too early to take off. If Menchov is good, he will be able to counter every Di Luca attack. If Sastre goes and Di Luca seems to breaks, he will surely follow Sastre to gain more time. I don't think Basso has shown he is strong enough to ride away, but this could be his possible day of glory, if he can follow Sastre.
I don't really expect the attacks to begin from the start, but more or less around 6-8 km before the finish, full out.