You might not think that making a payment app "social" will be enough to carve out new space in mobile payments, but Venmo expects to try. First of all, Venmo will make it easy for users to review their history of payments. Second, Venmo will allow users to share the history with other people.
When you go to pay someone in Venmo's app, it automatically assumes that you want to share your payments (the what, not the how much) with the world on its site and your Facebook account. The social aspects of Venmo are its major differences from PayPal.
In some ways, its an analogy to "check in."