I just got one, and these are my very first impressions, after just a few races.
First, the bad: The controller is, in fact, recognized as a controller, not as a wheel. This means there's a noticeable dead zone, which is unfortunate, but not the end of the world.
And also, the trigger buttons you use for accelerator and brake are calibrated weirdly. They are at 100% at mid-way, and the rest of the travel is just wasted. This means that the throttle in particular is very sensitive, and will require some getting used to. This is annoying, but I'm getting used to it already.
The controller has a sensitivity adjustment for the wheel turning, and you can also affect this with the controller sensitivity setting inside GT6, but there seems to be no way of adjusting the sensitivity of the triggers.
Then the good: The wheel feels nice and it works. It does afford a lot more control over the car than the standard ps3 controller. A definite step up from a standard controller.
I own a big Logitech GT wheel, and I'm quite sure it's going back into the closet. It's better, of course, but not enough so to justify the space and hassle it takes to set up.
I played forza 4 and forza horizon with microsoft's wireless wheel thing (similar to gioteck), and that one is awesome. It's the best controller for me. I prefer it over a full wheel. The gioteck is not as good as that one because of the two inconveniences mentioned above, but it's still decent, and as I said, a step up from a normal controller.
Opinions subject to change once I get more than an hour on it.