I'm quite pleased with the "understeer" model. It's quite easy to see how one can take advantage of the poor tire model in both F1 2011 and GT5.
There's a lot more going than that which meets the eye - without slip angle being modeled graphically (though it may be in some degree from a physics perspective) steering input being used in-game compared to steering angle allowed and present in reality is hard to judge. However, watching a good amount of hot lap videos shows how easy it is to take advantage of a tire model that rewards the idea that more steering input yields more turn-in. Compare some of the fastest hot lap videos to real onboards and sure, the lap times, car-track positioning and gear changes line up. But more often than not, turn-in seems massively overaggressive. It doesn't end at turn in either, mid corner, speed scrubbing steering angle is easy to find. Who can blame them? If the model rewards this driving style with low lap times, why stop?
A huge difference for a formula 1 car comes in the area of aerodynamics. Codemasters are trying to capture that difference, i.e. GIGANTIC drop-off in tire grip levels as the speed is reduced, especially at hairpin, +100kmh turns. Unfortunately, a move towards this idea hasn't been received well on the interwebz.
Now I'm not saying all of the fastest hot laps on GT5 and F1 2011 are poor, overly aggressive, unrealistic attempts that fall short of reality. I'm simply saying: maybe a Formula 1 car is an understeering pig when several thousand pounds of downforce are suddenly gone.