I'm interested in getting access to a full WHOIS database in order to expand on a domain-profile project I'm working on. I know ARIN provides this database only to non-commercial researchers and every WHOIS provider I know of (including ARIN itself) has rate-limiting.
I also know, however, some commercial services that already exist (like the registrant lookup section of domaintools.com, which can search for domains by registrant name) which are impossible unless the site has direct access to a cached copy of the WHOIS database.
Any idea how they got ahold of their data?