This is a really clever idea: Link Feedback tracks people linking to you and delivers a list of those people back to you, using only a invisible gif and a little javascript. The two portions -- one, collecting info on a central server where the application runs; two, delivering information to each visitor with javascript -- have been around for a while, but this is the first time I've seen them in use together, and in such a good way too. I wonder what else could be gathering and provided on a per-visitor basis? And since the server is central, is there an application which utilises this as an advantage, to distribute information too? Hm.