I was banned from Digg for violating…
"…to advertise to, or solicit, any user to buy or sell any products or services. It is also a violation of these rules to use any information obtained from the Services in order to contact, advertise to, solicit, or sell to any user without their prior explicit consent;"
…because when I posted a comment on Digg, I included a link to my blog. It's really pretty convoluted I guess. If I wanted to get a link to my Blog on Digg, I would need to pay them, in cash to advertise. Why would I pay them? Because my advertisement would be seen by people, who might go to my blog and might buy my album. That is valuable, so I need to pay for an ad.
Why do people go to Digg? To see the ads? No. People visit Digg to read the content and the comments. At which time they are exposed to the ads, that they might click on and give money to the advertiser. So the content and comments are the commodity, produced by the users, which generates income for the advertisers, who transfer part of that income to Digg.
So by me placing an 'ad' within my comment, I broke the flow of value, from the users to Digg (in the form of content and comments) and to the advertisers and then to Digg again.
Granted my comment was formulaic and not particularly interesting, but did possibly add some value, yet my expectation to receive a return from that value broke the Digg terms of use.
Digg is smart.