I thought it would have actually been a core feature of OSClass. I mean how cool would it be if it could detect your location based on your IP address. of course the user would have the option to change that location, but it would be a great improvement if the location could automatically be filled in, or not allow the user to choose a location at all.
Such as a site I am developing. It would improve workflow if the user didn't have to type in a location everytime. I don't want the users to be able to choose, I want the IP to find their location.
It's a relatively simple idea, but you get the point.
UPDATE:
Doing some research I found IP Info DB
http://www.ipinfodb.com/ip_location_api.phpI am integrating it into my website, but I don't know how I would make a plugin version of it, currently it is only in the theme, auto-filling in the boxes. It would be cool if someone could do some javascript/jquery magic on this.