While I don't really care about 'thin' as the current lineup is plenty thin enough for me, a 12-13" MBP would be good for me. The screen real estate is not as big a deal as I think I will be switching to using my laptop as a desktop on the road, setting it on a desk and hooking it up to an external monitor. More important to me would be the feature set, if they can match the feature set(Not integrated graphics, FW800, etc) of the MBP I would likely be sold on it as 17" is not portable, 15" is but I think I owuld like to try a smaller for my next machine.
Seablade
Doing has every now and then pop in.