Well I can shed a little light on this. If it is Adsense, they will eventually catch upto you. I know plenty of people who have been banned from Adsense. I highly respect the Adsense network and therefore would never cheat it. Adwords itself brings alot of traffic to my other sites and is definately something I support.

Any other network I really dont care about, they are all second rate crap in comparison. The biggest issue people have is not creating enough impressions through normal traffic, not spacing the clicks, not spending enough time on the site you endup at, and not cycling the Proxies enough.

My advice, if its Adsense then stop, if its anyone else, just be warned that someone will eventually realise and your cheques will stop coming.

The other thing is to remember that networks with no real reputation to defend will not care even remotely asmuch about what happens. They only care about money which is what a good CTR brings, and therefore some even secretly support cheating.