Kudos to Jay Small for sharing discoveries from a carefully test of registration models at Scripps newspaper sites.
In a test at 13 newspaper sites, Scripps modified the so-called threshhold -- the number of "free" pageviews a visitor is allowed before being challenged for registration or login -- and carefully measured the results.
Skipping to the bottom line: A threshhold of 3 to 5 pageviews allows "drive-by" traffic from search engines to be satisfied, while still capturing most of the value of a registration as regular users are induced to provide personal data.