Also, I love the approach with close integration with mails - I think it is strange that the mail protocol isn't more widely used - having my own copies of the conversations, easily searchable and exportable, is a huge advantage!
Email is in some ways like a whole hidden social internet. A lot of people use email who have no interest in Twitter, Facebook, etc. And many of those people are really interesting. Radiopaper provides a way for them to have public conversations online without having to learn a new technology, and without having to worry about what might end up associated with their online presence in the absence of active management.
I share them with a political party that I disagree with, and it always irks when I am called by them.
Maybe I should create an account and check if there's a setting before I whine about it... but this is still the internet!