I thought that trying to keep up with Drupal development was bad. Constantly changing APIs, functions parameters reordered, but at least that was once or twice a year. Facebook is even worse!
I've recently written a facebook app, ShiftBuddies, for the company I work for, Computerminds, we had some nice functionality that would show different content on a user's profile block depending on whether you were the profile's owner, or a visitor.
But no Facebook has changed their policy and show everything to the profile owner, and have a much more restrictive set of options for showing different users different content.
They made this change and gave us developers ten days notice. They have also taken a step backward: In the old days if the user didn't have permissions to see some content, they'd not get the content delivered to their browser. Now everyone gets everything, and it's hidden with CSS. So now we get lovely white spaces everywhere!
I think these changes are less motivated by user privacy, and more by reducing the load on Facebook's servers.