In 2003, I did a project called Channel Z. Its goal was to build a blogging tool that made it easy to categorize stuff. So easy, that I would actually do it. And if I did it, maybe I could figure out how to get other people to do it.
I'm the kind of guy who likes to categorize things. I made a tool, an outliner, a long time ago that makes doing that very easy. I still use the outliner to this day, and love it, and I keep finding new ways to use it to be more organized. With excellent results.
Okay, so how did the whole categorizing blog posts thing turn out? It was a bust. I would start out with a burst of energy but then get busy with something more interesting, and would never go back to it.
Being stubborn, I hacked some more to make it even easier. Came up with the idea of a text router, a right-click menu that instantaneously categorized the bit of text I'm pointing to. Couldn't be easier. Right-click, choose a category, save. Boom.
Dan Bricklin explained it as follows. "Instead of making you feel bad for 'only' doing 99%, a well designed system makes you feel good for doing 1%."
So apply that to Circles. You might feel a rush to organize your friends into categories when you start to use it. But you'll give up after a dozen or so, as soon as you hit one that defies categorization. You'll say to yourself "I'll come back to this later." You won't.