nomis5 - 10:28 am on Aug 6, 2013 (gmt 0)
Once every six months or so by accident.
I did initially report the first couple of clicks many moons ago and actually received a response from G effectively saying please don't waste our time telling us about it, the odd accidental click is to be expected.
I suppose the context is also important. If you normally get a couple of clicks a day and click one of your own ads then they might take some action. If you get a couple of hundred clicks a day and click one of your own every six months or so then they will take a different view.