Its very hit and miss, not something I would build a service around. In my circle of 4 friends, it only had data on one of us.<p>One big flaw is that you can't provide multiple sources of data as the basis of a search. Eg no phone AND email, only o ne at a time.
At first I was skeptical about fullcontact, afraid of the big-brother like effect.
Then I met the CTO at a hackathon, and it turns out he's really concerned about privacy and respecting opt-outs. I highly recommend the company.