What's being made available? Updates, photos, videos, notes and comments, says the Wall Street Journal, but only if you allow access. We'll be interested to see if such access is provided as a single privacy setting on Facebook ("anyone can mash up my updates"), or done on a case-by-case basis like Facebook Apps and Facebook Connect - the latter is far more likely, and the WSJ appears to confirm it:
To take advantage of the new services, users would have to allow the companies to receive access to their Facebook data, according to people familiar with the matter, and users' privacy settings on Facebook will extend to any new services built.
And this, I think, is the reason Facebook's open ecosystem, despite its 200 million-plus users, may not kill off Twitter's traction with developers: Facebook's culture is one of privacy and shared updates with friends. Twitter is all about public updates, and hence users love for you to mash up their Tweets into public-facing applications like TweetingTooHard.
Twitter is Still More Open