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 an interesting question actually; I guess at some point, if there is sufficiently advanced AI (I should use the word 'information retrieval' to not instigate a tangential discussion on if AI is possible) in a search engine to identify and link personal information, does a search index constitute a 'database' per Directive 95/46/EC?

The author of the original article could write a paper on it :)