You may have always heard how you can geographically pinpoint where an email came from using IP address but now GeoTool makes it possible for the layman.
Simply enter in any IP address and click. The GoogleMaps mashup shows where that IP resides.
In more robust email systems, you can find in your toolbar an option called “view message source” that will help you figure out the IP(s) of the sender(s) (which, for the unitiated come in the format something like 126.96.36.199, four sets of 1-3 digit numbers seperated by three periods).
Nifty for determining where the spam is coming from, who may have sent you that anonymous piece of hate e-mail, or whether your online customer service has been exported to Pakistan.