The client library allows users to make Facebook API calls from any web site and create Ajax Facebook applications on that website.
Wei Zhu from Facebook explains the benefits:
Since the library does not require any server-side code on your server, you can now create a Facebook application that can be hosted on any web site that serves static HTML. An application that uses this client library should be registered as an iframe type. This applies to either iframe Facebook apps that users access through the Facebook web site or apps that users access directly on the appâ€™s own web sites. Almost all Facebook APIs are supported.
I find this very interesting for several reasons. The first of which is that I’ve recently read a lot of articles talking about how blogs are really one of the largest social networks in existence. While Facebook makes it obvious, our blogs basically represent who we are, our abilities, and our interests. We have implied relationships (like friends) on our blogs thanks to our blog rolls and the people we link to frequently. But, unlike our Facebook pages, we have the ability to customize our blogs and really take control of our little space on the internet. Moving from their sandbox social network out into the real-world is a really interesting play.
Also, since you need a developer API key to use the Facebook APIs and you can only get one by being a member on Facebook, it opens up a lot more opportunities for Facebook to data mine everyone for advertising purposes.
I for one will not be putting Facebook on my blog, but I think it’s an interesting idea that may rattle the cage a bit.