Found this in another forum and thought I'd post it there, too:
http://www.pir.org/faqs/whois_limitation
http://www.pir.org/faqs/whois_limitation
Why is PIR limiting WHOIS Port 43 access for the general public?
PIR is committed to protecting the rights and privacy of registrants of .ORG domains. In an effort to reduce access by speculators and data miners of WHOIS Port 43, and based on consultation with ICANN and registrars, PIR will introduce rate limiting logic on the WHOIS Port 43 server on 20 August, 2005.