Not by Adsense directly, because they don't tell you - they just give you 'that email' But banned by a domain parking company that uses Google's adfeed. I was banned yesterday, saying my traffic has little or no conversions - so they decided to ban me. This is kind of bs. I mean publishers shouldn't necessarily, automatically be banned for this.
If your traffic isn't converting for the advertiser when compared to other sites, why do you think the advertiser would want to pay for your clicks? If there are no advertisers, there is no PPC.
Unfortunately this is the way of the world. You have to put your own considerations first and build assets. For instance, if you built a product related site and monetized it with Adsense, you could easily switch to another ad provider. If you choose a subject that is hard to monetize with anything but Adsense, you have put all your eggs in one basket. Worth thinking about. Dean.
I was banned from an affiliate network for little traffic... such things seem common out here. However, I've replaced the affiliate ads with Adsence (and the numbers show 3-5 times the impressions, but *shrug*) and I do not think that Google will be slapping me around with that email anytime soon.