I've had the odd bit of fun with an Evo, P-Car, F-Car and even once a bike - not at the lights, but on the Motorway (Freeway to those readers across the Pond). I think as long as the road is quiet and it's done in a friendly way (I always let them go past at least once and do the thumbs up), and not at silly speed for sustained distances it's fairly harmless.

I always pull away from the lights really slowly when kids are looking for a burnout contest in town - a) dangerous and b) reinforcing the stupidity as MMD says. Never (so far) had any real nutters yet - 911's are two a penny in London, so thy're not regarded as that flash anymore (unlike Ferraris)!

SoS.