Do you remember "Caitlin Roran" from Gmail's promotional pictures. These, Gmail's fictional characters are now at Facebook. Someone spotted Caitlin Roran and Nathaniel Woodward in Facebook's privacy page. Go to Facebook privacy settings, then choose "Custom" and click "Customize settings." Under "Include me in 'People Here Now' after I check in," click "See an example." You should see some of your friends, plus Caitlin Roran and Nathaniel Woodward.
Probably it's because, Paul Buchheit, the ex-Googler who created Gmail, is now a Facebook employee and he's not the only former Gmail engineer who works at Facebook. According to Christopher Harley, Caitlin Roran is a fictitious name used by Ana Yang, while Nathan Woodward borrowed Casey Muller's photo. Ana Yang and Casey Muller got married last year.