SSMS really is the best option out there for those who want to fly a Shuttle on their computer. I got into an argument with a guy on O-F.com over this, and it is just clear that SSMS is able to do far more than the Shuttle shuttles can. From the displays, the implementation of the GPC, the switches, the systems, RMS arm which is the best simulation of the arm I have seen anywhere.
I have never hesitated in recommending SSMS 2007 to anyone. And with the new features, it should become a must have for anyone even remotely interested in space and manned space flight. One thing that always seemed to throw people off when they first tried it from those coming over from FSX, is that switches can only be thrown in the 2d panel, and that the key mapping is different (mainly the F keys for changing view). In FSX people get used to picking just the 2d or just the 3d and not having to switch between the two.
But with the new 3d flight deck, that curve is now gone, and I think a lot of people will find it will add greatly to the immersion of the sim.
I can't wait for v2 of SSMS, but of course you already knew that.