At some point, it's up to the product. If you can't succeed with that much exposure, the product wasn't right. People didn't get it, didn't care or didn't want it.
Circles (and other ideas, some going back to wave) is more like goals than ideas. The goal is to have different categories of friends to control what you see, and who sees which of your stuff. You still need an idea for achieving that goal.
Google's idea put too many confusing choices in users hands. It's like the difference between Gmail's search-centric UI and outlook's folders.
Folders are great, if everything is in folders. Search works no matter what, no inbox management necessary. The folders that work best, work by default too (updates, promotions, junk...). No sitting down and pondering how one would like to use email.
Google's "idea" for achieving their goals was asking users to think of how they'd like to use this thing they've never used before and do some preparatory work, like categorising friends they might connect to in the future.
Abstract questions are always harder than they seem. Asking users to create abstractions is tricky.
