I saw one video at google about a guy showing some basics of driving a manual gearbox, and then there is a bit where he drives GTR2(i think) with a G25, and shows what happens if you drop the clutch while in gear... The car jerked violently like it would in RL, it looked cool, didn't know you could do that, i only play with auto clutch in sims...
It probably isn't soffisticated, ie doesn't work in other gears, etc, but it's cool..