Heads up: Google does this with Gmail, too. http://news.cnet.com/2100-1047_3-6050295.html - "Judge grants subpoena and orders that all e-mail messages, including deleted ones, be divulged."
Best advice I ever heard (and it came from an ex-Facebook employee), "treat communication ("private" & "public") on all services, including Gmail, Facebook, and Tumblr, like a million people are listening."
"We Are Building A Web Where The Default Is Social" - Mark Zuckerberg
Mark Zuckerberg is dead set on making Beacon work. This is his latest attempt by making the apps do their dirty work by asking for a permission and auto-sharing.