Based on the demo you can only put friends in one circle, but I hope that's going to change or just isn't properly reflected in the demo; I have plenty of people I would consider to be in multiple circles. The easiest example of which is a "co-worker" who is also a "friend".
Oddly enough, I hope this maps to the gmail groups concept, since I already have people mapping along those lines in there, and winds into my android device as well.
Google seems to run into the large corporation octopus issue where knowing what the left and right hands are doing is a difficult task.
