>The concrete difference is that on Facebook I follow friends and coworkers, on G+ I follow Scoble, Tim O'Reilly, Alton Brown and other people who write interesting, public posts.

With Facebook's new follow feature (released this week) you can follow those people on Facebook as well.

Facebook even partially solves the Scoble problem by asking you if you want to subscribe to all, some, or only the most important posts from a person and Blake Ross has mentioned that they may be doing further things to help filter what you see on your wall (perhaps classify posts by subject?)