One possible upside is the Metafilter principle: If you charge $5, you get a higher quality signal by excluding a lot of chaff. The probability that your search

One possible upside is the Metafilter principle: If you charge $5, you get a higher quality signal by excluding a lot of chaff. The probability that your search engine user is human gets much closer to 1, and you save a lot (but not all) of the anti-abuse effort. This gives you better signal on which websites are interesting, so you need possibly orders of magnitude less data to do a good job.