Drat, I guess that it's too late for "tear down that wall" speeches. Facebook is waay out ahead. Heck, there are even VCs devoted to Facebook Apps.
And Bebo throws a gantlet as well ...
Bebo Launching Platform: "The Bebo Platform is nearly 100% compatible with the Facebook Platform: the APIs, markup language, and query language are all the same."
So started the Social Graph Platform Wars!