ThinkProgress has a video showing Palin reading from carefully scripted talking points during the debate. Unlike her interviews with Gibson and Couric, this was an "open book exam."
UPDATE from Marc Ambinder:
Debate rules prohibited candidates from bringing any pre-prepared material with them. Only blank paper and writing utensils were provided. So to the extent that Palin seemed to be reading, it was because she had, during the course of the debate or during Joe Biden's answers, written down some notes. Clearly, she had memorized talking points and wrote them down when she got to the podium. But that's not what's being alleged. Biden did the same thing -- you can see him jotting down some notes and then referring to them before speaking.