Dopplr is a social networking application for travelers that I always thought someone should build. You tell it about your travel plans and it tells you which of your friends are going to be in the same place. It's low tech - no automatic GPS updates, just good old-fashioned manual posting, but it's simple and effective. They are adding users slowly by occasionally giving existing users a few invitations to hand out. The process by which those invitations materialize is rather mysterious, as is everything about the site. The "about" page does not mention any names but refers to "an international team" in Helsinki. They do solicit feedback but don't answer their email.
Two names do occasionally pop up on the Internet, Matt Biddulph who says on his blog that Dopplr started as a part-time project but is now his full time job as CTO, and Marko Ahtisaari, an investor. Until recently, the domain was registered to Daniel Gillmor but has recently been changed to an anonymous proxy registration company.