Now what would be really nice is if there was a similarly-easy-to-use "notifymewhenitchanged.com". Every change-notification site I've seen thus far has required a cumbersome signup process.
The data actually already exists for this. The Wayback Machine stores caches of website data, you could do simple checks for changes, and then report back any significant differences. Possible statistical site could be built to show the highest-moving sites based on the changes to their content.
There are a few things to do this, I personally have used Feedwhip a bunch. The guy who writes it is really nice and they have both email and RSS options. http://www.feedwhip.com/