While doing a site with lots of custom node types for a client, I decided to isolate some features into a generic and reusable module, and the favorite nodes module was born. This is a relatively straight forward module. The admin chooses which node types to enable favorites for, and users with the correct permissions see a link saying "add to favorites" at the bottom of the node. When they click that link, the node is added to a list of their favorites.
An Open Source Content Management System (CMS)