Looking for a social network to deploy my concept

I have (yet another) concept for social media (don't worry, it's cooler than all the other ones). And I am looking for ideas about where to deploy it first. The market group is 18-35 yr olds who are willing to spend money on technology. Within that group, I am looking for networks that are neither too loose nor too tight. Here I define a loose network as one where any two people that meet are unlikely to ever meet again by chance. I define a tight network as one where everyone already knows everyone else, and in the worst case, no one is reaching outside of that network.

I'm looking for examples of networks that are in between these two extremes because I think that this is where ideas will spread more rapidly. I think the best case would be one of these "in between" networks that is loosely connected to other "in between" networks.

So any ideas for real-life networks like this? (By real life, I mean in the flesh as opposed to online.)

Just in case you're interested, here's my other question on networks.

You are looking for real life networks?

• Clubs at Universities
• Gaming clubs
• Computer clubs
• Programming clubs

You can find places these groups actually met up at www.meetup.com

A bit older more professional networks
- Chamber of Commerce Mixers you can not know anyone and feel welcome. Or know everyone
- BNI - Business Networking Institute you have to be a member and it becomes tighter the longer you are in it
- Toastmasters is a loose network where you go regularly, but the age can be a bit higher

Online networks
- MySpace younger and loose
- Facebook young & old but tight
- Twitter mixed and loose

You can find all kinds of Networks online and physical at www.ning.com