Pure awesomesauce! :) Congrats on name pivot, Circular is a great choice.

With regards to Buffer, a potential friction point I pointed out to the team earlier this year, was the inability to select:

Who? (Friends, Public, <custom list>) and

Where? (private message, private group, wall post) a message should go to.

This is standard functionality in the Facebook sharer app, for example. (http://imgur.com/HPsXU)

Of course, Buffer and Circular adds When? (eg temporal dimension) to the mix, but no app I know of, has implemented all three, leaving you with a tradeoff, if all of those are important to your social workflow.