Trust me...they happen <img border="0" title="" alt="[Eek!]" src="eek.gif" />
Like Julie said Yahoo has groups that focus on this...and I mean a lot of them. Here in Chicago there is one group in particular that is small in size but high on the reality. They screen all people that enter the group (singles and couples) and is run by a swinging couple. I've never had a chance to attend one of their "meetings" (which on a good week could be once or twice during the afternoon during the week followed by Friday night, Saturday afternoon/night, and Sunday afternoon...yes they are active <img border="0" alt="[ROFL]" title="" src="graemlins/rofl.gif" /> ) But even is this screened group you run the problems of spurt of the moment/planned GBs i.e. no shows, performance issues, lack of "eligible" women. This group is starkly different than the gangbang I viewed previously as the women are treated with the utmost respect and care and in the eyes of the attendees...everyone there is just there to enjoy some outrageous and extremely fun sex. No demeaning or nothing.
On the other hand the gangbang I did view was in conjunction with a party thrown by another yahoo group. Now I saw view because I walked in (after the warden/hubby asked me first if I had a condom in hand) to be greeted by a naked woman giving a guy a blowjob while easily 10-15 guys waited around (and the second woman involved cleaned up in the bathroom). In this environment both the men and the woman to me were viewed as meat. After getting an eyeful I walked out...right around a used condom or two laying on the floor.