I use the DS3 for B-spec only.
I agree with Mr Green. I was using the DS3 all the way up through about level 25 aspec. Recently used some best buy rewards coupons to pick up the logictech driving force GT which they luckily had in stock. And can honestly say that driving with the DS3 now is depressing and almost not fun.
I regret not picking up a wheel sooner. The first few races were a little rough with it, definitely a different beast than using the controller. I tried driving around some higher powered race cars right off the bat (minolta 88, FGT, etc.) with horrifying results. Did some test runs with lowered powered cars (cappuccino, civic, etc) and slowly got used to the feel of the wheel and pedals.
Just last night took the IMPREZA Sedan WRX STI spec C Type RA RM '05 around nurburgring and it was intense and so much fun throwing the wheel back and forth around those tight section. Just an amazingly rewarding experience going through sections clean and fast with a wheel versus a controller.
With a wheel you just have so much more control of the car and makes the game more fun than I thought it could. $150 for the DFGT is a steal for the enjoyment it has given me.
As for worrying about a special set-up I'm waiting for a driving stand pro to come back in stock, but I'm using my ironing board with fantastic results. Its stable and height adjustable so it works with almost any chair.
So for all of you rocking a DS3 more power to ya, just don't get a wheel cause you'll never go back to that DS3

. For those of you on the fence about getting a wheel hop off and get it, just be prepared for a few hours/days of poor racing till your adjusted.