Ok guys, you heard it here first. Within 12 months, Google+ will have a lot more active users, simply because they will start counting all Android users, Google Play users as Google+ users.....
Facebook, here comes Google+!
Edit (a few hours later): Sorry, I should have given more context. I was just listening to the Google I/O keynote. Google has added Google+ login APIs. While this is similar to FaceBooks ability for people to login to FB and use that ID everywhere, since Google owns Android, they can provide app owners some more benefits - e.g. prompt the user to download an app.... Anyway, soon, it will require some work for Android users to not be on Google+. Given the growth of Android (900M+ users today), there will soon be more Google+ active accounts than active FB accounts (IMHO).