Fab Swingers is now up to 5000 members, mostly UK swingers but there is also a growing number of Irish swingers.
The site is a free community site so there is no marketing budget and all of the members have come from word-of-mouth recommendations. So although it's not the largest swingers site (by a long way!) it is mainly people who really are into the scene and who have probably been introduced by friends. And 5000 members in only 8 months isn't too bad!
It's also quite unusual because Fab Swingers has pretty much equal number of couples and single men registered; most swingers have vast numbers of single guys and comparitively few couples. Again, this has happened because the site has been built up through personally recommendations of couples in the scene.
If you'd like to give it a go you can sign up at http://www.fabswingers.com