The Pulse site will behave a bit like Threadsy or the desktop app TweetDeck, aggregating real-time updates from Facebook alongside other social networks.
Yahoo has been trying for months to make itself the ultimate starting page for Internet users; you can already view your Facebook and Twitter feeds using Yahoo's "Quick View" feature, but Yahoo Pulse will provide an improved, tabbed interface and offer new kinds of integration in Yahoo and Yahoo Mail.
Notably, Yahoo Pulse will have a privacy menu that will apply to multiple services. That feature will be an important draw for some users, given that Facebook has dealt with a big privacy backlash in recent weeks. Just don't expect it to add completely new privacy features to your Facebook account.
The privacy angle is also pertinent when you consider that Google — Yahoo's chief rival — made some major privacy errors that greatly hindered the launch of Google Buzz, a very similar service. Those faux pas and the lack of Facebook integration prevented Buzz from becoming a killer application. Pulse is Yahoo's answer to Buzz; maybe it learned from its rival's mistakes.
The specifics of the new interface and integrations have not yet been revealed, but it's all expected to launch within a few days. We're curious to hear what kinds of integrations with Facebook Yahoo users would like to see, so let us know in the comments.