Nick Wilsdon has posted an interesting blog post about just what Google knows as a Domain Name Registrar (which it became in Feb 2005):
believe Google has built or is building a tool to analyse domain names. The API access they were given as a Registrar allows them to carry out the level of automated queries they needed for this. I would also go further and suggest this tool is building up a historical picture of each domain through regular scraping of their WHOIS records.
Read the rest of Nick’s blog post.