At the risk of being unique, I honestly don't believe this is a problem or something people need & want in order to return to a site. Usually, if people want to talk to the same people on multiple sites, they let it be known themselves - either in personal conversation or by posting links to their various sites. A lot of people (most?), actually like to start fresh in a new place, particularly when it comes to blogs/journals.

Personally, I never use any of these types of options, on any site. Putting a lot of time and resources into a 'find people you know' option seems like it would be wasted effort to me.

I think to make a site 'sticky', the emphasis only needs to be on interesting content, ability to search for common interests & interesting content, and creating a welcoming atmosphere so people feel comfortable starting their own conversations/posting their own content, (and an attractive, easy to use interface). All of which DW does really well already. :)

Sorry if that's not helpful, but that's my honest experience and opinion on it.