Review my project: SitesInCommon
pedalpete: I can't say that this is the site that I've been looking for, but you might be on to something.However, you have a bit of a catch-22 with respect to the sign-up vs. experience this without signing up.I didn't sign-up, and therefore, you can't show me anything. 
You also don't describe anything on your home page, so I don't know if sign-up means I'll need to download a plug-in, no plugin, do I need to tell you how it works.A good way to demo it for people is to maybe show how many people near them visited your site? They don't need to see the person details. Maybe a 'here is what's popular near you' list, or something like that. Just to get a bit of interest going and show that you have some data.I think a big thing you've done wrong on your site is the 'these people both read ...'. I don't care what they read if I don't read it. Therefore, if you can show me how it relates to me, that is likely a better avenue I think.