If you've got a Facebook account, you're going to start seeing more websites that want you to use it. Facebook now allows you to "like" web pages that aren't part of Facebook itself. You'll also be able to use your Facebook account for an increasing number of websites.
These changes are part of a sweeping change to the way Facebook works. Now the social networking service will use "like" buttons used by other websites to pull in information about what you are reading, watching and doing on the web into an "Open Social Graph". And companies that partner with Facebook—such as Microsoft, Pandora, and Yelp—will be able to use your Facebook profile to provide you with personlized services.
For example, let's say you've "liked" a band on Facebook. When you go to Pandora's internet radio site while you're logged into Facebook, it will pick up your profile information—and then suggest song mixes, or "stations", based on those bands.
Yelp can use your profile to set up an account on the restaurant and entertainment site, and you can click "like" buttons for restaurants and other places you're fond of. As with other sites that now sport the Facebook "like" button, the information on what you've chosen as something you like ends up back on your profile wall.
Microsoft is using this capablity for a new site called Docs.com, a shared document site that will compete with Google's GoogleDocs offering. It will let you upload or create Microsoft Office documents, and share them with your Facebook friends.
Along with the changes that Facebook has made to make these things possible come new privacy concerns. Websites that use your Facebook credentials will now be able to access your personal data from your profile for longer than the 24 hours they were previously limited to. And more of your data will be public, by default—it's up to you to restrict what other sites can access.