An article that I wrote for Coding4Fun (a Microsoft hobbyist programmer website) has just been published:
In the article I show how to create an ASP.NET page that displays your eBay Watch List. All the data is pulled down using eBay Web services, and you can extend the app to do any sort of wacky manipulation that you want. Getting the data from eBay is really easy -- turns out the most difficult thing is manipulating the "time left" information into something that is user friendly. Go read it, and enjoy!