me and a mate went to an airfield track day earlier this month in an old seat leon tdi. it was the best laugh i have had in ages. and the added bonus was that we both got loads of passenger rides in a variety of well sorted cars (ex time attack r33, 700bhp supra running 2bar boost, caterhams, exige etc)
this is something i would recommend, but be warned... its expensive to do it. average of £120 per day to run, then factor a pair of tyres, fuel, and if you unlucky, repairs. the leon we went in did 4 tyres (we wiped out the 2 fronts with understeer, then swapped front for rears and spent the last 2 hours laughing like mental patients at crazy lift off oversteer!!) oh yeah the leon also lunched the head gasket lol!
one other factor to think on. there are tight noise regs for most track days. if you turn up in a motor that is too loud then you will be asked to leave the track and no refund. 2 people fell foul of this on our day.