There was an article on PezCycling News where they interviewed a Garmin-Transitions mechanic recently. The answer he gave:
"At the Giro, every rider had one race bike and two spare bikes, plus we had six riders with two TT bikes and the other three had one TT bike. Our bikes are all more or less pretty standard. Mr. Millar uses a mechanical Dura Ace group set on his TT bikes as he can get more extension with the gear levers. Tyler Farrar uses mechanical Dura Ace on his road bikes as it has a more positive clunky feel in the sprint, which he likes. "