A web index is not the same thing as a database about people. The original blog post explicitly says he built such database, he didn't just mirrored Google's data.
It's not illegal if you get the necessary permissions from the privacy agencies (which will ask things like: how is the data stored, do you do join with other databases, can a user ask to have its information removed, etc.).
(IANAL I just happen to have dealt with that kind of things when building a lobbyist database out of public documents for an advocacy group)
Edit: removed part about database rights, lets not complicate the subject.
It's not illegal if you get the necessary permissions from the privacy agencies (which will ask things like: how is the data stored, do you do join with other databases, can a user ask to have its information removed, etc.).
(IANAL I just happen to have dealt with that kind of things when building a lobbyist database out of public documents for an advocacy group)
Edit: removed part about database rights, lets not complicate the subject.