I have used green screen a couple of times.. I am not a big fan. You can get decent results, but I just find it better to use a limited number of backdrops and use gels on my lights to alter the color.
To me, greenscreen almost always looks photoshopped (though, I am sure there are few people out there that can do an amazing job.. )
I use the Greeen Screen and have reasonable results with it. The only real problem I have is with those fine little hairs turning green. Let me know if you want more dialog on this as I have several months of experience with this. I also have a bit over 2600 digital backgrounds.