I posted here because I thought you guys might have some tips for further refining the estimate and some ideas for other sharing sites to include besides webmail sites and facebook and twitter. Also, I make the claim that most apps that send direct traffic are "sharing" apps - email, twitter and facebook clients, RSS readers. Can you think of any apps that might lead to large amounts of direct traffic that aren't necessarily "sharing" apps?
Why doesn't Fred Wilson log into his bit.ly account and look up the click stats?