I think this idea may have been mentioned before, but it's a useful way to find domains associated with an IP address, etc.
http://www.enyo.de/fw/software/dnslogger/ http://cert.uni-stuttgart.de/stats/dns-replication.php
(The links were forwarded to me.)
It's probably similar to what whois.sc is doing for their fee-based reverse IP lookup service. But they probably have more sensors.
http://www.whois.sc/reverse-ip/
Jeff C. -- "If it appears in hams, then don't list it."