As long as not everyone has facebook I'm not sure this is a big threat to other people search startups. As long as personal information is still spread over several websites having one place to go search for people that indexes all of this third party data (including Facebook or LinkedIn) is still a good thing. Now if Facebook were to go start indexing third party data on people and make that searchable together with the personal data that they store that would be a big threat. But I'm not sure those are the intentions of Facebook. I think the recent move is primarily used to attract more users to Facebook. You can see if some of the people you know have accounts and then decide if you should sign up. When you have 30 million users you can take advantage of that to attract more members.
