College students signed up, found nothing of interest and didn't bother to visit again. I'm fairly certain that G+ has failed, but I can't say I didn't expect it: Circles, its main selling point, is a gimmick that no normal user would bother to use after day 1, the UI is rather unexciting, etc. As far as I'm concerned, there's really no incentive to switch from Facebook for most people.
Not directly a citation, it is very hard to dig for a "bounce" rate or usage statistics of Google with the deluge of the real-name debate in content searching.
