Instead of capturing full frames, it's scanning from top to bottom at 24fps. It's fine for static shots, but as you introduce motion, or fast moving subjects, you get a "jelly" effect.
I have a friend who does highend visual effects. In his experience, the RED also isn't suited for green screen work. Can't remember off the top of my head if it's for rolling shutter or the dynamic range, but it's another limitation.
However, it hits a sweet spot for less demanding productions, like The Social Network.