For those who do not understand the economic incentives associated with social graphs, have a chat with Facebook, LinkedIn and Palantir. Or read about the reasons why mobile platforms were forced to implement access control policy for contacts, after apps began bulk-uploading valuable social graph data.
They (OWS) were recently subpoena'd for someone's data and all they could provide where rough timestamps when that user registered and when they last contacted the servers. Unless you think they're lying in response to a subpoena (which would be very serious from a legal perspective), then they really don't store that data.
Of course it would be nice if we didn't have to trust them that this won't change in the future (whether through a court order or their decision doesn't really matter).
