Well for the first time yesterday I spent a decent amount of time playing GT5P on my G25, and it makes me really hope things change for GT5. As mentioned, the feeling of weight transfer is completely lacking. There is no sensation of the car settling on its suspension in a turn, you just turn and it turns and you straighten and it stops turning. Turn from one direction to the other quickly and you can induce oversteer, but there is none of the sensation of the weight transfer occurring, it's just like it happens because that's what's "supposed" to happen. Another big gripe is turning into high speed corners, if you lift off the throttle to get the car to rotate, it does rotate, but at the same time it goes wider... Oversteering should tighten the line, but what seems to happen (in a couple of the cars I've tried at least) is the back end comes out, but the front end also loses grip and you slide sideways to the outside of the track. And this is going at a speed where not lifting the throttle would have kept you on the track, but you're lifting the throttle to tighten your line. Instead the opposite happens....
In some ways it feels worse than GT4 to me, it's just not playable because the most basic inputs don't always result in correct outputs. I really hope it's significantly improved for GT5. I have a PS3 and I'm not gonna spend the money on an Xbox just to play Forza 3, so GT had better get it together :P