I do a lot of green/blue screen stuff at my full-time job. I am very used to lighting keys and rendering good-quality keys in post. I cut w/ Premiere Pro 2.0. Sometimes I do the keys in PP2, sometimes I use AE.
Recently I was brought on to a freelance gig to assist a inexperienced shooter w/ a key. Basically a guy drove past the camera (left to right) in front of a giant green screen. The guy I was working for insisted on shooting in 720 24p mode. The motorcycle moved past the screen at a decent clip, which in 24p resulted in a choppy-looking drive-by. Now, I'm trying to key this in post. It's just NOT working for me. No matter which frame I use to try and set the key, the biker is blurry. Is the fast-moving object shot in 24p preventing me from obtaining a good key?
With only 24 frames per second, the lens is open for a longer period of time, resulting in motion blur. And the choppiness? 24 frames per second doesn't handle some rates of motion well. For example, certain panning rates yield choppiness in motion.
You can still possibly key this stuff, but it'll struggle at areas of blur between the screen and the motorcycle. There's a chance you'll have to go in and do some roto to fix it.