That means Diaspora has 370,000 users right off the bat. Impressive? Yes. But even if those 370,000 users all also quit Facebook and delete their accounts (doubtful, imho), that's still a drop in the bucket compared to 450 million. Most Fb users wouldn't notice any change in their social graph, certainly not enough to leave Facebook.
Further, Diaspora's pitch is great at getting tech geeks like us to fork over money, but it includes nothing that real, mainstream users actually care about (that is: talk to your friends, share photos and videos, play games... and maybe, just maybe, control your privacy). Think about who the average Facebook user really is. They're not people who know or care what the term "data portability" means, and Disapora loses them as soon as they use the word, "node."
In reality, Diaspora is like Identi.ca or Diso. They're great ideas on paper that we (tech nerds) may love, but mainstream users could care less. They go where their friends are, and right now, their friends are on Facebook. Facebook might eventually damage user trust enough to make people want to leave, but a pitch about data portability and open source is not going to get them to switch.
