It would be really cool to utilize the XFN standard. This can help Brightkite share and work well with other social sites. In case you are not familiar with XFN it could be a simple as:
hyperlinks to my page would include a rel='me' tag.
links to friends could would include a rel='friend' tag.
Digg and Twitter currently use XFN. And I can see many aggregation apps looking for it. I just saw a presentation by Don Park who spoke about XFN and a XFN spider he wrote. Very interesting.
http://gmpg.org/xfn/
donpark.org
I really like the site and am excited for you!
Jed