The circles are what Twitter lists tried to do, I think, as well as Facebook’s limited profiles and groups — but Google pretty much nailed it on the head, here. I think the management of the circles are a large part of the vibe, in fact.

As with anything, there is still room for improvement, though. What’s interesting is that there are other burgeoning (and some defunct) social tools that already hit upon that idea, and they even integrated Facebook and Twitter. They simply can’t (or couldn’t, in the case of the ones that have shut down) compete with the weight that Google can put behind their system, though, especially when integrating everything into the Google products infrastructure.