I am checking out an email tool that looks pretty interesting -- xobni. I have been using Facebook more lately and have been thinking about how email and Facebook are similar types of systems. There is a social graph, a good way to communication async, and a sense of dealing first with "who" then what. I pretty much always read the name of the person before I think about the contact/mail message. Same in Facebook.
Have you used xobni yet? What is good about it? What is bad? Do you use facebook too? How are they different?
Here is a link if you want to check it out.