I see on the forums a lot of folks reading my review and others that caution on performance, and making a decision not to buy FSX until the tweaks are refined, or there is a patch, or they get a new machine. My recommendation was (and is) that if you’re unsure you download the trial version and give it a shot. Performance varies a lot from machine to machine (and I think even the ACES aren’t quite sure why the variation yet), and you might be able to adjust settings to make it enjoyable. Keep in mind that the demo areas are not as detailed as major urban areas, and your performance may vary.
And to the request by many for MS to provide a patch: they are already committed to a new Vista/DX10 version next year, and hopefully that will include some bug fixes as well.