Can't play this game on a controller anymore. Played GT4 and everything prior on a controller, and one day bought the DF Pro. After a long learning curve (boy were my times SLOW on the wheel at first!) I've stayed with a wheel since. I've only ever played GT5 with a wheel (I've used controller here and there when I don't feel like setting up the driving rig, but never could survive in a race environment). Upgraded to a DFGT down the line thanks to craigslist, and have been using that since.
When I first started out, the wheel was mounted to a snack tray like everyone else. Wobble and slide galore. My first stability attempt involved strapping weights to the snack tray. Minor improvement. Next upgrade was a chair, a box, a shelf, and a bunch of free weights and twine. Basically I made a little weighted diving board to mount the wheel to. This helped greatly with the stability of the wheel, but in either situation I found sitting that high/upright was very unnatural with the pedals, and I'd wind up floating my feet over them and pressing more down like a truck driver than forward like a race car driver, plus I'd get shin cramps/splints eventually.
Next setup was much better but still not permanent. Used a massage chair (in the pics below) that was much closer to the ground to sit in. Put a kitchen chair on either side of me, and put a shelf across the seats. Weigh down the ends of the shelf on the seats and it was pretty decent. PITA to setup, break down, move, get in, get out; but held the wheel *fairly* stable and seating position/pedals were much much better. No more leg pain!
Now that I was in a more natural position, I was racing a lot more often, and the effort involved in this setup took it's toll. I decided it was time to ditch the chairs and weights and shelves and actually build a rig to hold the wheel that would be somewhat collapsible. Searched around a few different forums for ideas and plans, went to home depot, and built what you see below. Made using hand tools and a dremel, I spent about $45 at home depot for all materials including a hand saw and miter block combo for $15 (one of the best moves I did that day was buying that saw & miter block!) Prior to that, my other option was a hack saw.
Now that I was racing more and more constantly, I found out that lack of lower back support in the massage chair was taking it's toll on, well, my lower back. One morning I woke up so stiff and sore I could barely move my torso at all. That has now been replaced with an
Audio X Rocker I had sitting around doing nothing. I stuff some bumpers under the rear to prevent it from actually rocking and I'm set. It's a real comfy chair (although I admit I do still use a lumbar pillow on it when racing), has pretty decent audio if you want to pump through it, and is a great chair for other gaming when I'm not using the wheel.
So yeah, bet you didn't expect such a long answer to "what everyone else is using" but that's my story and I'm sticking to it!