http://www.leadsexplorer.com/ and http://www.net-results.com/ both offer website visitor identification software that appears to do more than just basic whois lookups. They're designed to show you the business name and website url of corporations visiting your website, and sometimes appear to work even when the publicly available whois information says something else (such as the name of their domain registrar or ISP). I was wondering whether anybody had any idea how they work in the latter cases? Incidentally, you can try them out yourself, as both platforms offer free trials. Analytics experts, please advise!
There's only so much information they can gather. One additional header that is often passed on but not reported is the proxy header, which can sometimes give you a clue as to which company the person is coming from.