We all know people are banned daily because of click-fraud, people clicking on their own ads. Often, people deny that they clicked on the ads - and I believe most - but Google needs to protect the integrity of the network. :)
A thread at WebmasterWorld named Banned for Somthing Other Than Click Fraud? Some listed responses:
- Connection with other banned accounts
- Inappropriate content
- DMCA claim against a site
- Hopefully, scraper sites :)
Forum discussion at WebmasterWorld.