The light shone on that dark corner of the internet (see my Framed! post, as well as Tim’s Framing Lauren linked post) and it brought results. If you haven’t read my posting, go ahead; there’s too much information to usefully summarize here and the comments are good too.
After reading all the comments that came in (including some private email), Tim and I chatted a bit with Paul Hoffman, noted IETF/IMC heavy. A likely explanation (as pointed out by many commenters) is that the purveyors of the “aff” sites were probably trying to run an affiliate scam on the Adult Friend Finder site. They probably chose my site to frame because Tim has a high Page Rank and often links to my site, and thus my Page Rank is also reasonably high. Paul checked and found that they were doing their own name serving, hiding themselves quite effectively from us (well, given more time and effort I’m sure Paul could have dug up more information, but it didn’t seem worth it).
I posted my piece on Saturday and Tim pointed to it not long afterwards. By Sunday afternoon the “aff” sites were noticeably slower and seemed to be going off the air. The last referrer I had to my site was from site 23 on Monday December 18th at 10 am local time; pinging the address shows it’s still there but there is no longer an http server attached to it. The site is still in the Google index but I expect that to go away at some stage as well. So they reacted quickly; I expect we will never know the entire story. I’ve learned two things though: keep a closer eye on my access logs, and post about things that look weird.