Just one click wont do you any harm, but i believe Google keeps in record total number of such clicks over a period. So I would suggest you to report to them in the link given by forestorm. I wont do you any harm, but may help you in case of any contingency
ive done this a few times, because i actually saw an ad i wanted to visit. i never got banned for clicking around 8 times over the course of a few months. but then, i read up on the TOS and stopped doing it. Good thing too, i hear google has been banning a lot of people lately.