Google recently introduced the option to control how much of the content from each of your circles appears in the main stream. Until now, your main stream would just show every post from every person you've added to any circle. This can be a drag if some of your circled people are very talkative while others aren't. Now though, you can go to each circle and adjust the amount of content from each one that shows in your main stream.
The odd thing is that it's not clear what the percentages are or why you'd only want to see "some" entries, but not others. For me, the value is in the all/nothing approach. I've just reset my circles so that, for example, all posts from UMN folks show in the main stream while posts from folks in the Following circle don't. I put people in Following because I'm interested in what they have to say, but now it doesn't hide material from people closer to home.
To adjust what shows in the main stream, go to any individual circle and move the bar as directed.