I race the ARF's and have made virtually no modifications... they pretty much work great "as is". I did replace the aileron inner tube with a sullivan (yellow) inner tube... I've had no binding problems and not enough slop to notice at all. I've seen some guys do away with the single aileron servo arangement and mount a servo for each aileron out on a wing bay. Probably the most important thing you can do is make sure you get some washout in each wing (just follow the instructions - they call for it). Like Barry wrote, most of our guys fly the arf and generally very few mods (if any) are made. They're plenty strong and fly great.
Clark