Follow Me, Follow You

I noticed a lot of people have been circling me on Google+ lately. More than usual. I must be posting good content. I haven't circled back any of my most recent followers as I've been traveling and haven't reviewed them yet.
What's the criteria for getting a reciprocal circle? You have to also have good content.
An empty stream doesn't tell me anything about you or what you normally post about. Any mention of your SEO business or that you're a "social media expert" kind of disproves your claim. Only reposting one other person's content, which I have seen, doesn't get you circled; it gets them circled. Also, I use Reader, so a stream full of posts I could just subscribe to, well, you can probably figure it out by now. I look for interesting new content and analysis. Post about your articles and videos, for sure, but also go behind the scenes on the stream. I try to supply interesting content and I'll circle you back if you do too.