I'm quite active on Google+ since July. Thus far I have 3916 people circle me there. I post a lot of ARM related and general tech related posts, comments and opinions every day. You can circle me here: https://plus.google.com/106075758531242552855
I believe Google+ is already far better than Twitter and Facebook. These are my stats on each platform:
I think Google+ is going to get even much better as soon as Google implements clever recommendations algorithms for your stream. Based on your +1 ratings it will be able to display "People who +1 the kind of content that you +1 also +1 this content:", thus filtering out the randomness and listing only the interesting posts automatically. Every good post will automatically get the deserved audience, more or less regardless of who is circling who.