Great question.
I think that the Ducati have significantly raised the bar again with the GP09, and that Stoner is ecstatic with the feel of the new CF chassis. Vale will rise to the challenge, and it will be very close- hopefully going down to Valencia again, but I see Ducati prevailing this year.
Meanwhile Haga looks very comfortable on that <strike>1098</strike> big bore 1200 thingy. He's completely adjusted his riding style to harness the mid corner speed and torque of the big twin, and for the first time in his career looks smooth and flowing. He also salvaged two good results at Qatar, a track which hasn't been kind to Ducati in the past. He's lost his favorite circuit in Brands, but is .... hot at Monza, Kyalami, Assen, and Brno. This won't trouble Spies in the slightest, who I believe is more talented, composed and consistent, and the new R1 is a revelation - Yamaha to win.