this is pretty cool
I already have blocked a couple of the big guys in my Windows host file.
For example this entry blocks all ads and tracking when using MSN messanger:
0.0.0.0 rad.msn.com api.bing.com
This blocks tracking from a popular track site:
I used to browse with Fiddler on to see what extra hits my browser was making in the background and I snipped a couple places using that, but this is going to be a big help in finding some more.