My current T prepares extensively - it's obvious that he does, and I've also asked him about it - but I have seen Ts who clearly did not. T sometimes forgets things I've told him, because he can't possibly read all his notes from the past four years every time, but I've noticed that when he has been unclear on something he'll always read up on it in preparation for my next session. He also checks out books, music, and occasionally even films I've mentioned, if he thinks they are relevant to my therapy, and he also keeps up with current research (but that's not just for my benefit, naturally).

I think it is part of a T's job to prepare, and I do think it's unfair on the client if a T is constantly badly prepared and doesn't review their notes.