Yes. There's Diaspora and Frendica already, with maybe a few hundred users.

To launch something like this, you need to figure out some way to get a user base, a user base that people will want to connect with. Something like

- Ivy League students (hey, it worked for Facebook.)

- VC, angels, investors, and startup CEOs. (They might like something with more security, especially since they might be planning to take a bite out of Facebook or Google.)

- Political groups, where there are communities of fund-raisers and lobbyists, people trying to get things done together and concerned with others not listening in.

Consider targeting groups that involve people working together to do something. They need to-do lists, spreadsheets, scheduling tools, and other collaboration support. Basically Box.net's feature set, but without Box, Inc.