On the PEX/PEP1 threads was an ad for the "4 Foot Farm' which I was curious about. It goes to a cute animated chalkboard video ad. The site gets IE security certificate warnings, and I wasn't about to enter my credit card info, although I would have checked it out for the measley $7 if there had been a PayPal option.
Some of the ads we are currently running at permies come from google adsense. They use algorithms to scan the thread and figure out which of their ads would be the best fit for that page.
There have been some ads where I thought "that is awful" and I can go into adsense and say "don't ever run ads for that domain".
Of course, the flip side of that is that what we all want is for all the bills to be magically paid and there are zero ads. Although I very much like the idea of advertising stuff that is very much aligned with this site. Cassie has been working on that. Maybe someday we can get in enough advertising that is well matched that we can eliminate google adsense.