I have'nt modded mine yet as i still have about a year left on my warranty, but once that runs out, i will be adding a new wheel, new shifter knob, new pedals and will also put a mod in the brake pedal. I forgot the name, but its a small rubber block that you can put in the brake pedals spring. Apparently, it adds ALOT more resistance and feels great.
P.S O/T, G25 is soon going back to logitech. Damn shifter has broken for the SECOND time.