Doesn't the whole 120Hz mean that your PC has to render at a solid 120FPS constantly for the 3D to work?
That would mean that you'd be pushed to upgrade more often to make sure the latest games work in 3D so your games run at 120FPS.
I'm one for the Eyefinity, I would have loved to get a TH2G and a third screen, but the resolution restriction of TH2G was a massive offputting, I've tried softTH too, and while it works, the lack of dual GPU support also put me off.
Eyefinity appears to be the best of all current solutions rolled in to one.
No.
Just like you don't need solid 60fps for games to work on a 60Hz LCD.
120Hz divided by 2 angles alternated for each eye for the glasses so you will get 60hz full refresh & see a maximum of 60fps just like 60hz LCD monitors.