I have not played GT4 yet, but as soon as my finals are over i'm getting it and going to use it as a tool to help speed up my learning of the circuit layout for when I go in September!

Having been to the ring in real life (and having more than one braincell) I know it cannot replace putting in real laps, but all people did before GT4 was watch videos again and again to learn the circuit before they went (Watty?) I don't see how GT4 is much different!