Try arin.net for IP searches
http://www.arin.net/index.shtml
Enter the IP in the Search Whois box in the upper right column. If you select the Search button with no IP entered, a page with general information displays.
It's probably not enough for your purposes, but it would give their ISP name (and country?) or their own server like RB.
I routinely use this to determine when vendors for "American" companies are actually working in foreign countries and using a U.S. phone exchange for a foreign call center.
It also indicates the hosting company (per the NameServers) - if the poster violates that company's Terms of Service, a complaint to them makes a point, as well.
Per my subscription e-mails - Received: from host.ronpaulforums.com (host.ronpaulforums.com [67.225.158.146]) Two other IP addresses in the e-mails related to BlackHole, presumably spam filtering.
I do notice that the IP address of my network card in my modem seems to be captured by online registrations, so that may be more of a unique identifier (particularly in the event of illegal activity/police investigations) than my Yahoo/Gmail IPs.
NOTE: That also means you can identify the same person using multiple UserIds to bypass a prior banning.
Big brother at work
