In the next phase of its better to ask for forgiveness than permission approach to new features, Facebook has modified its controversial Beacon program to be opt-in instead of opt-out. There is still no way to opt out of the entire program, but now each time a site is about to send an announcement back to Facebook the pop-up asks for permission instead of assuming no answer means yes.
I suspect what motivated Facebook to act was that some merchants, such as Overstock.com, had suspended their participation until Facebook changed the program.
Louse Story has a detailed account of Beacon's evolution in the New York Times, and Brad Stone has an interview with FacebookVP Chamath Palihapitiya who reiterated Facebook's philosophy of trying out features in the market instead of in the press:
A. “One of the things we try to do is listen to feedback as much as possible. Just to give you where a lot of this feedback is coming from, it’s coming more from the press than specific users,” he said. “Right now, the right thing to do is to make sure we speak to actual users, not the pundits.”