I realize that Google+ is supposed to be a ghost town. There are a number of online articles comparing the Google+ to Facebook as if the two were equivalent.
Let's be clear, Facebook is a social network. A place to leave short messages to your friends and play games together. Google+ is a platform or infrastructure. Google+ has a social aspect with its circle mechanism but it is not simply that.
The latest upgrades have taken Google+ to a brand new level and I suspect are the reason the stock topped $900 yesterday. Integration with existing products has been improved and I like the new clean look.
Since I use it heavily for sharing photos I was pleasantly surprised to see improvements to the photo search algorithms. Here is a graphic outlining the latest changes.
Google I/O 2013 Announcements by trendblog.net