I've been driving with a wheel since day one. When I bought my PS3 back in 2008, I ordered a G25 at the same time. I'm now using a G27 and I'm just waiting for for an official release date from Thrustmaster for the H-pattern shifter and I'll be ordering a T500RS.
I don't just play GT5. I play other PS3 based racing games and I also play PC based racing sims. I'm looking for the most realistic experience possible. And to me, using a wheel is an essential part in that experience. The few times I tried driving with the DS3, I was completely hopeless. I could barely control the car, let alone set any competitive times. But that said, I don't really play any other games outside of racing sims so I have almost no experience with the DS3. For me it's basically a device to turn on or shut off the PS3 and navigate the XMB. It's a foreign object that still doesn't feel quite natural in my hands.
Owning a wheel, especially a mid or upper range wheel is not cheap. And for many people on this site, who are still students, or struggling in a bad economy or for whatever reason, don't have the financial means to buy one, I understand and sympathize. I was there once too. But I can't quite understand why people wouldn't WANT to use a wheel with a driving game, if they could. In my opinion, it's the single most important step in bringing a game like GT5 away from gaming and that much closer to a sim racing experience.
Real cars have real steering wheels. (Not DS3s)