The way that the media is describing it is quite entirely different from what you are used to on websites.
A lot of ad agencies - ya know those that provide the ads for your websites - e.g. Google, Yahoo, AdChoices (Microsoft), adbrite, and so on. Most of the major companies don't do it, and even if they do it, they don't give away your info. The only thing that's shared is the metrics - such as how long you read the site, stay on the site, the clickthroughs, the pageview, if your computer is unique, stuff like that. But other companies, like independent advertising firms - they do it 10 times worse, and if you stumble across an unknown company, they do things more evil than the ones that are large independent firms. These other companies sell your information [doesn't matter who's bidding for your info, it can be anyone, but most common is companies, corporations willing to pay big bucks to that agency] - and that means everything from your age, your address, your preferences, the whole marketing sheet. Those firms make money off how much they can learn from you browsing.
The large ones don't sell your information, they do it by the law, and by the book. If they don't do it by the book, they get in trouble.
Facebook is doing it entirely different from other companies. Facebook is putting your "timeline" in plain sight. This will just cause trouble for Facebook, because users don't really want to share everything. They want to share, sure, but not everything.
If Facebook is that evil - Expect your previously visited websites to appear on the timeline and charge each shared website for putting their metric on 100 million eyeballs.
