I don't doubt that 60% of people use it daily. I personally click on that +Mladen button a couple of times a day at least. But I'm not so sure that they are using it in the same way as Facebook or Twitter.. that is to say for personal communication with their friends.
None of my friends are on Google+. But there are tons of really smart people that I don't know personally (although I wish I did), who post lots of great content for me to read, and consider and discuss. With this personal experience in mind, I believe the 60% are using it as a content discovery platform, not so much as a social network.. sort of like another Reddit/Twitter