I just got an invite to Google+, the new Facebook-like offering from Google. So I created an account, and at first glance, I would say Facebook and LinkedIn have a lot to worry about. Note, however, that Google has a very mixed track record of success outside search and mapping. Anyone remember Orkut? It never caught on the U.S., although it has been successful in some other countries like India. If Google can do a better job of supporting business-oriented uses of Google+, both Facebook and LinkedIn will have to work very hard to keep their customer base.