Very easy to implement. IP2Location gives you 20 free lookups per day. Would be nice to be able to click the IP address on a users profile to see IP information. Should be quite easy to implement as a link.
http://www.ip2location.com/<IP ADDRESS HERE>
Would be cool, but I think this would be better off as a plugin due to the limitation factor.
@luke Not sure how you'd apply this as a plugin. If I knew that, I'll throw it together.