"One more barrier is gone when it comes to you and me federating," said [Kim] Cameron. The significance of federation is that applications can work with multiple identity providers. Geneva lets you create web applications that authenticate users against both your directory service, and those of partners, even if the web server is outside the corporate network.
...Geneva is set for full release in the second half of 2009. It has the potential to solve real problems in the enterprise and deserves more attention than Microsoft has given it at this PDC.
I suppose the last statement is just conjecture, but the Geneva framework looks like it will do a nice job addressing some of the problems developers will run into in the cloud-based development world.