Building a system where you input an e-mail address and it spits out likely friends of that e-mail address isn't exactly the same as having pre-built "shadow pr

Building a system where you input an e-mail address and it spits out likely friends of that e-mail address isn't exactly the same as having pre-built "shadow profiles" for a bunch of e-mail addresses. With such a system it would be trivial to build a social graph for a person quickly after they sign up for facebook (and then suggest friends). But, doing so doesn't necessarily mean facebook had previously built out a social graph for that e-mail address and had a profile waiting for it in the shadows.