Hi Josh,
Please don't take offense, but shouldn't you focus on getting gContactSync rock-solid working with gmail contacts before adding major new features like syncing with external services like myspace/facebook?
I really, really, really would hate to see gContactSync die a horrible death because you tried to do too much too fast with it.
Personally, I will never, ever have a facebook or myspace account, and would *much* prefer that you simply add a native on disk file format and then provide the ability to sync with a local filesystem and/or an FTP server.