If you're a frequent reader of Aaron Wall's SEOBook (which is a good idea for anyone in this business), you've probably seen his super cool link-hovering graphic that shows the popularity of that particular outbound link as compared to the others on the site. Personally, I think the feture is pretty cool, but what's even better is the service that powers it - MyBlogLog.
MyBlogLog offers incoming and outgoing tracking so you can see (through the addition of a single line of Javascript code) how many people are coming and going through which sources. It's a very, very cool piece of work. I have a 3-day trial turned on now and I'll make sure to report back with specifics and numbers at the end. The best part is that it's only $25 for a whole year through Paypal. I think I'm sold.
I am running it on one of my hub sites and plan to use the data in two ways. This site has hundreds of themed outlinks and I plan to cut some of the links that do not generate interest. Will also try to develop some on-site content for the most active links. This could also be used to experiment with the anchor text to see how that changes clickability.