I doubt that it would be able to run smoothly enough to enjoy. You'd probably have to set everything to minimum and then reduce them some more.
In saying that, I haven't seen any definite benchmarks. A completely maxed out MBP (3 gig ram etc.) could probably run FS9 pretty well along with some add ons and whatnot ... FS X is still a big question mark. Wouldn't it be great though? Flight sim on the go!
I wonder what X-plane would be like on a MBP (anyone?).