Toshiba Portege R600 here. I imagine the size should be fine, as it is slightly smaller (in all dimensions) than the X200. Weight is what you pay for with this one - only weighs slightly over half as much as the X00
Have found screen size and battery life excellent, and the keyboard no trouble to use for a full day in remote offices. 3Gb ram is also good. Have never had a problem with Toshibas.
Have used in Y on a 737, and ironically compared notes with the gentleman seated next to me, using exactly the same model! (He thought the speed was a bit limited due to the low voltage CPU, but I don't find it an issue as I don't expect an ultraportable to be the bees knees in performance, or use it for anything greatly more complicated than basic office functionality, email and a bit of photoshop).
The price is the drawback - way over the others mentioned here.