Adsense Ethics - Stealth Advertising Techniques

Adsense and other contextual advertising systems offer small webmasters a chance to get a "slice" of the advertising revenue pie. You don't need to have a gigantic web portal or millions of page impressions a month to get enough cash to cover some of your basic costs, such as domain registration or hosting. Those of us who run larger websites are able to make more money - obviously. We are also interested in seeing how we can maximise our revenue without falling foul of the Adsense TOS. However not all webmasters are ethical and have resorted to using techniques that could be described as extreme, borderline or creative depending on your own stance. Darren has an interesting summary of some of the techniques being employed and you can see why some of them would attract attention. You can also see how they may help increase revenue. The question remains though - is it worth it? How far will you go?