Active steering: corrects you if you 'steer too much'.
Example: you use steering wheel. When entering a corner you whack your steering wheel to the left. Because you steer waaaayyyyy too much, you actually loose grip.
Active steering corrects that. You can turn your steering wheel all the way to the left, but when you check a replay you'll see that your wheels are not max turned.
If you set this to high, the PS3 will correct you to 'the optimum' steering angle.
As far as I'm concerned, active steering is something that can exist in real life, hence I do not see it as a 'cheat'. Mind you: a pro driver who can 'feel' the wheels will automatically not steer as much, and will be close to drivers using 'active steering on strong'.
SRF however is a totally different story.
SRF imho is a cheat.
What it does is: give you 30% more grip, by increasing the programmed grip setting of the game. It's not something that exists in real life.
Example: you steer into a corner, driving waayyy too fast. Lets say the car understeers.
Lets say you could corner at 100km/h, but you try it at 120 km/h.
You will not make the corner. But with SRF on you gain 30% more grip the moment you loose grip, so you can corner it at 120km/h.
As far as I can tell it's about equivalent to increasing tire compont 1 set 'better.
So, if you use Sports Hard, without SRF you can turn at 100km/h. With SRF you manage to do it at 110 km/h.
But, if you turn SRF off and use better tires, in this case Sports MEdium, you're also be able to corner at 110km/h.
However, if you turn SRF on you can do it at 120km/h (equal to Sports Soft without SRF)
I drive the BMW M5, max tuned with Sports Soft and all driving aids off around the Nordschleife in 6:45:xxx
With Active steering on, I'm not getting faster. Stays at 6:45:xxx
With SRF on, I can suddenly do it in 6:35:xxx.
Conclusion:
SRF does not exist in real life, it alters programmed physics of the PS3.
Active Steering could exist, but dunno if cars have it the way GT5 is doing it.
I don't mind people using AS, but I don't like people who are fast drivers and still use SRF.
*edit: numbers may vary and are examples.
But I seem to remember reading '30% more grip' somewhere..