Extract from Facebook's announcement:
"Now we also want to share the benefits of our work by enabling other social sites to use our platform architecture as a model. In fact, we’ll even license the Facebook Platform methods and tags to other platforms. Of course, Facebook Platform will continue to evolve, but by enabling other social sites to use what we’ve learned, everyone wins -- users get a better experience around the web, developers get access to new audiences, and social sites get more applications."
Bebo already announced that it will focus its efforts on applications compatibility with Facebook (while continuing to support Open Social).
Are we heading towards a format war between Google and Facebook?