Kev, at least they're discouraged on site now (which they really always have been unwritten-like). Ever been to a dirt kart track? All that is is tire prep. Learning what combination of chemicals to rub on the tires and how long to take the torch to them to get them right. There's definitely an art, and if someone were to have individual sets of tires for accel and skidpad they could probably pickup a tenth or two, with the same compound (we had a good 40 Shore A swing between 3 different sets of the same compound of tire).
Other than the bafflingly complicated ETC rules and sound limits that have already been discussed, the only one that really confused me was the 45 degree tube bracing rule. Could someone diagram that? It really doesn't make any sense. Which plane are we talking here that it can't be out of skew with?