'Pneumatics', as they are called, have been banned in almost all clubs down south, definatly every one that I have been to.
They have been found to be a massive advantage, and any vibration problems described by Tropi are not significant enough to outweigh the advantage down the straights. Also, the air cushioned tyres tend to give really good grip.
Down here it was done by glueing the rims on both sides and soaking the tyres in oil to make them expand.
Luckily it's really obvious to tell, because the tyres are squishy. If you suspect someone of illegally using pneumatics then simply take a pin and slyly pop one side. It's far more entertaining than simply disqualifying them.
McLaren