Ray has informed me of a service which will tell you the geographical location of an IP address. It is hostip.info. I thought it was interesting and useful. You can do things like:
http://api.hostip.info/country.php?ip=12.215.42.19
US
http://api.hostip.info/get_html.php?ip=12.215.42.19
Country: UNITED STATES (US)
City: Sugar Grove, IL
http://api.hostip.info/get_html.php?ip=12.215.42.19&position=true
Country: UNITED STATES (US)
City: Sugar Grove, IL
Latitude: 41.7696
Longitude: -88.4588
There is also a Firefox plugin. I thought this was going to be useful until I noticed that only 50% of those located are located correctly, according to a survey they have on their site. Although this may be true, it may also be true that this could help in finding virsuses and the such. It appears they are also working on a Thunderbird extension.