It's hard to know why this game works so well, but the genius of Zuma or Tetris or Angry Birds inheres in the smallest details
The most important circle in Google+ might be this one:
That's the reward that you get for playing the casual game that is at the heart of the Google+ experience. When you go to add a friend, the service presents you with a series of rectangular tiles with people's names on them across the top of the screen. At the bottom, there are several circles into which you can drag the tiles. As you do so, the circle pulses to life and when you drop the person into it, the green +1 circle drifts upward. This is a classic way of indicating a game reward, as in, say, Super Mario Brothers. A number drifting upwards on the screen means, "Points!" The +1 indicates not just that you've added someone to a circle, but that your high score just went up.
I think this explains why I've been compulsively pulling tiles into circles for the past few days, despite never having had the urge to create Twitter lists or sort my Facebook friends.
It's hard to know why this game works so well, but the genius of Zuma or Tetris or Angry Birds inheres in the smallest details. There's something brilliant in the way objects teeter in Angry Birds or the way the frog ball shooter thing rotates in Zuma. The way the +1 floats up in Google+ isn't quite in that league, but it's still great -- and a hell of a lot more useful.