Reports surfaced yesterday, and now we have the official word from Facebook. Users will now have to opt-in to share purchases via Beacon:
Stories about actions users take on external websites will continue to be presented to users at the top of their News Feed the next time they return to Facebook. These stories will now always be expanded on their home page so they can see and read them clearly.
Users must click on "OK" in a new initial notification on their Facebook home page before the first Beacon story is published to their friends from each participating site. We recognize that users need to clearly understand Beacon before they first have a story published, and we will continue to refine this approach to give users choice.
If a user does nothing with the initial notification on Facebook, it will hide after some duration without a story being published. When a user takes a future action on a Beacon site, it will reappear and display all the potential stories along with the opportunity to click "OK" to publish or click "remove" to not publish.
Users will have clear options in ongoing notifications to either delete or publish. No stories will be published if users navigate away from their home page. If they delay in making this decision, the notification will hide and they can make a decision at a later time.
Clicking the "Help" link next to the story will take users to a full tutorial that explains exactly how Beacon works, with screenshots showing each step in the process.
It seems like a win for users, although I'm sure the ramifications of this announcement will be dissected and considered in the hours and days to come. First impressions though: the immediate defaulting to privacy is sure to appease many critics, but the details may still raise some concerns, for example Facebook is still capturing this data, the only difference now is that it wont automatically share it. Will this be enough? advertisers will still be able to tap into Beacon for purchasing preferences and other details based on activity on Facebook so the privacy option is really only skin deep.