Grouper might be a little...um...different than GrubWithUs [1]. There's a little more of a feel of a "group date" rather than, "I want to meet new people." As somebody well attached, I would feel rather uncomfortable in a Grouper setting, but not in a GrubWithUs setting.
Grouper is in beta in SF as well. I've been on one and my friends have been on several. It was fun, but so far no one has made any friends (or started dating), so I don't know it's a solution to this problem.
[1]: http://blog.joingrouper.com/sex-in-the-bathroom-and-the-prob...