You can find the slides of our presentation of Rules attached to his post. The presentation has included a demonstration of a "Notifications" feature, what enables users to subscribe to changes of a node. I've also added the feature module we used, so you can use, share and re-mix it as needed. For the feature module to work you'll need the flag module patch for porting its Rules integration to D7 or just use the code of this sandbox. There is a video recording showing the slides available at the drupalcon site.