I liked them when I had a pair with my TNT1 @ 1024*768 res.
I never had any headaches from using them or ever felt sick. You can also, well used to be able to take screenshots with the double image and see it in 3d using the glasses. The reason I stopped using them was the lake of drivers for them, as at the time Elsa updated drivers for thier cards first and didnt care much for the other Nvidia cards. The botttom line is, some people hate them, while the others love them