I think it has a hugely weird ICK factor to it, but to each their own.
There's a chat room devoted to it on chatropolis.com along with many other fetishes.
Yahoo has a group devoted to it.
Humiliation seems to be a central part of it.
Some of it seems to be kink role playing, but there are hard core fetishists who advertise and hook up with a "bull" for the little woman and themselves. Some are voyeurs who get off on their woman belittling them as they get serviced by a "real" man. Some participate as subs. Into: Sloppy seconds, eating cream pies, or being totally denied sex by the demonic wife. Lots of, ugh, variants.
"Bulls" advertise too.
Some of the "cuckolds" on the chat room claim to be "straight" husbands but seem really closeted and are more fascinated with the equipment of the interloper than the wife is, if in fact these chat room guys are even married.
Yahoo's group has lots of pictures and testimonials, so that attests to a lifestyle swinger fringe. Incredibly unattractive people though IMHO, I'm warning you.