Whether topical circles would enhance or dilute G+ is a matter of opinion of course. You might be right -- I tend to enjoy deep dives more than most. But I see

Whether topical circles would enhance or dilute G+ is a matter of opinion of course. You might be right -- I tend to enjoy deep dives more than most. But I see no reason, either in functional integrity or in social practices, that topical circles would diminish G+. Those not interested would simply not use them -- this is true of FB groups and lists. It is incredibly difficult to achieve the network density and connectedness required to make a social network stick. Attention is in short supply -- witness Ning's failure to become the social network of interest groups. Perhaps it's not feasible for vertical and niche networks to match the success of the generic social nets. For this reason strikes me as in the ballpark to enable sustained topical conversations where the audience already exists, and where shared topical interests could augment individual profiles and deepen engagement.