I think open graph is going to be a bitter poison pill for Facebook, and once they see what users actually do with it they will have no choice but to cripple it. Though I'm glad to finally see Brad Fitzpatrick's open graph idea from years ago on Livejournal come to fruition.
Tucked away in the announcements was a policy change to allow 3rd parties to now store Facebook user data for more than 24 hours. Facebook now wants every web site to embed their widgets, so to do that, they have to make their data freely available. Facebook might be a far better walled garden than AOL ever was, a truly wondrous Hanging Gardens of Babylon; but open graph turns them inside out.
Now what's to stop the rest of the web from just looting all of Facebook's data?
Some will argue that this is a similar pattern to being indexed by Google—trying to lock down content backfires, because if you give it away, the traffic Google brings you more than makes up for whatever you lost. So too for Facebook—they get more traffic back by giving away data compared to forcing everyone to facebook.com.
Everybody knows Facebook will become the next Myspace(Friendster, yadda, yadda), even if nobody knows quite how it's going to happen. (Kind of like how everybody knew the housing market was in a bubble, yet kept playing it up.) Blowing open the gates on data sharing is going to hurt Facebook more in the long term, because it opens up new opportunities to leverage user data across the whole web ecosystem in ways which Facebook cannot control. It's inevitable that someone is going to build a popular service on top of Facebook's user data; structued in such a way that Facebook itself couldn't clone it internally without compromising their other products and partners. While this itself is great for users and the whole web, it's not going to be so great for Facebook.