I have an adsense account and have done for many years. I have never been banned or had many issues. That said, I have never made much money out of it either.
I now have a site that is doing pretty well (totally legit original site with completely original content) and I am at least able to cover all my server costs and a little bit more, thanks to adsense.
However, I have read so many horror stories about google just banning people and taking all their accumulated funds. They don't ever give you a reason, there is no real way to discuss the matter with them and the appeal process is clearly a joke. I have also seen that whenever they have been properly legally challenged (as in someone taking them to court), they have lost or reversed their judgement prior to the hearing.
I have just contacted google today as I noticed what I believe to be invalid click activity on my account (CTR has gone up to about 24%). I have notified them but, having checked the server logs, can't really help them much more. I am well aware that despite me not being at fault in the slightest, google could simply close my account and I would lose about $80. I would also be banned for life.
I am genuinely interested whether they are acting legally, particularly by withholding earnings, when they close accounts. It just seems that publishers, such as myself, are so vulnerable to some idiot just clicking adverts "for a laugh". We have no real way of appealing the decision or speaking to anyone - and then they take away OUR MONEY that we have earned though valid clicks in the weeks / months beforehand.