That sounds amazing. My nephew and I are currently romping through The Following, after having just finished the campaign on his save. (He reminds me via Steam messaging how scary this game is to play by himself lol) I don't see myself picking up the Tobii Eye Tracking, but I can just imagine how amazing it could be.
This looks like some interesting tech and would make this game even more fun to play. I finished the first campaign and then got the second and played through it as well. I just don't know how well this tech would work with my setup as I play on a 125 inch 1080p projection screen. I guess if I was to get this I would have to play it on my 24 inch monitor which is fine. I think I would like to wait and see if any other games use this tech it would not make much sense to buy this and only one game supports it.