It is always something I think I'd like to do but haven't yet. Probably as there isn't a local one, hmm that's no excuse I'd rather do one where no one could recognize me!
I did it twice in Battersea Park which is supposed to be the biggest one (I lost 7lbs training for the 1st one, the second I didn't actually do any training!! But I beat my first time..... )
I haven't done it for a coupla years, too much work now!