In this thread I want to talk about the AdSense "invalid activity" instant bans. I don't know if it's only about small publishers, or only non-US publishers, I'll just tell you my story about being insta-banned and losing about $150 for no reason.
I like making sites and sometimes they become popular. To give you examples, I have a blog, a unicode emoticon "cheat sheet" page, a gallery with cat photos, etc. Some of them are in English, some are in Russian.
I always believed that you should not focus on money, just do what you like to do, create really good sites that you'd be proud to show to your friends and family, and everything else will be ok. Apparently not.
So when my sites combined got ~3000 unique daily visitors, I joined AdSense and got them all under the same account. It took me more than a month to earn the $100 for the minimum payment, so I filled in my address details and started to wait.
It was already more than $150 on my account (just before the PIN-code letter arrived) that I got an e-mail that I have some "invalid activity" on my site (not even mentioning which one), so now I'm banned for life and all my earnings are taken back. Just out-of-the blue, no warnings, no nothing.
I never clicked my banners (and never suggested anyone to), and this was specifically "invalid activity" ban, so it has nothing to do with my sites content (they have another one for content, "violating policies" or something). I never had any traffic spikes (apart from some reddit links that became popular, but that was about +20% of my usual daily traffic). I could't login to my AdSense account to even see the amount of clicks (since I'm banned), and they disabled invalid clicks reports anyway (more on that [adsense.blogspot.com
So I sent an appeal, giving them all the info I can (reddit links, Google Analytics trafic data, etc), but 12 days later I received an e-mail stating "after thoroughly re-reviewing your account data and taking your feedback into consideration, our specialists have confirmed that we're unable to reinstate your AdSense account". Of course, they "can't provide any more information" about why I was banned and even which site caused that.
So please, if you consider using AdSense in a similar situation, search more about their unmotivated "invalid activity" instant bans. It is quite common (even mentioned on AdSense wikipedia page). Please be aware.