It is definitely troubling to think about this in the long run and how this entangles into search/email and privacy concerns...
And honestly I don't think the G+ users will want their Facebook friends to be on G+, same way that most users on Youtube have separate accounts from their Google/Gmail account. From the looks of this, G+ will just push away users from other Google services, and causing confusion.
I've been seeing Google differently since G+. Google, the global CDN and distributed computer, is a platform now. G+ is the frontend they're building on top of Google to bring all their Google-based services together.
Obviously they're getting people to commit to their social identities on G+ so they can meet their stated goal of becoming an identity provider.
The war is on between Twitter, Facebook, and Google and it has nothing to do with the number of messages or advertisements that can be served. It's the number of end user identities that can be authenticated.
And honestly I don't think the G+ users will want their Facebook friends to be on G+, same way that most users on Youtube have separate accounts from their Google/Gmail account. From the looks of this, G+ will just push away users from other Google services, and causing confusion.