- Before the site sends your information to Facebook, a small pop-up appears in the window. If you don't click it, or if you wait too long (20 seconds), it assumes you have no objection, and sends the data to Facebook.
- The next time you log in to Facebook's site, it presents you with the opportunity to not display the information to your friends. If you don't exercise this opportunity (like, say, you simply go and do what you went to Facebook to do in the first place), the information is added to your feed for all your friends to see.
Update: Apparently, Facebook has responded to the consumer backlash regarding their Beacon service, and so they will be requiring a user's "opt-in" consent on a site-by-site basis. However: they are still collecting all of this information for themselves. This is still an unacceptable solution, and is designed to get sites not to prompt a user before sending the information.