Bruno Blondeau has released Watcher'84, an automated web page watcher for Mac OS X. Watcher'84 monitors a list of favorites web pages and notifies the user when something gets updated on one of them. "It is perfectly integrated to Mac OS X, is very easy to use, and features smart algorithms to only retrieve relevent content." It is $15 shareware.
http://www.brunoblondeau.com/watcher84/
http://www.brunoblondeau.com/watcher84/