Im running vista64 and have no problems whatsoever except the dual core AMD + AH issue that pops up every once in a while, but that isnt's Vista's fault, every other game and program ive run works amazing.
I upgraded to Vista mainly so Im not restrained to 3 gb or less ram, and to take get full advantage of DX10. FSX actually runs better for me under vista than it did under XP by a very noticable margine (due mainly to being able to use the DX10 features im guessing)
Vista isnt all bad, unless you try to cram it onto an outdated system, but hating it is really popular now, so if you wanna go for the "informed non-conformist" look, stick with XP. Or if you REALLY wanna be badass, go lunux or mac, probably have a fit making AH work smooth, but BOY wont you look COOOL.