I am awfully new to this game, but I do recall seeing a url shortener which enabled additional tracking to the initiating user. For example, showing the time distribution of the clicks along with originating sites. I may be stretching this a bit far, but just for the heck of it, if I wanted to figure out which social networking website had a larger pull for me in distributing information, this type of service would allow me to do that. (don't ask me why? :) )

The way I would build a business model around a URL shortener would be through those types of value add services which would draw users back to the site (ad-revenue, or potentially in-depth "pay" analytics), in addition to the already-mentioned resultant data insights.