I'm sure others must have done this in the past, but this works for membership building on either dating or adult sites, and could easily be adapted to more mainstream members sites too.

1) creating a micro site that mimics your main site and stick it in a sub dir like

http (membership).yourdomain

2) make sure sub directory you made is password protected
3) Start posting, chatting and giving out the login and pass .

4) make certain to give them a tease but build upsell into your micro site.
5) you will be amazed at the links and traffic you start getting inbound to your site.