ZoomInfo, which has been around for a few years and is aimed at corporate and executive search claimed to be profitable, and generating cash through subscription revenue. Wink and Spock are aimed at the bigger and more general consumer markets and need to be supported to some extent by advertising. These two companies are not at the money making stage yet, Wink is live while Spock is in invitation-only beta. Also, they are not going to generate a lot of money from direct search advertising judging by the numbers that were bandied around.
I think that a general people search function is most useful as an adjunct to a large internet company like Google or Yahoo that generate much of their revenue from advertising. People search is used to get demographic information about the user which is then used to target the advertisement. At a Business Intelligence SIG meeting last summer we heard about how Yahoo is targeting banner ads based on demographics, and it is no coincidence that Yahoo already has its own people search feature.
The CEOs of Wink and Spock both protested that they were pure people search companies that could survive and grow as pure people search businesses. However there was a general murmur in the room that everyone has their price. We will just have to see how it plays out.