A new article published on the Learning jQuery blog explains the intricacies of event delegation and the new .live() jQuery method. The event delegation (a great feature) allows you to declare a single event that works on numerous children of the same parent (instead of binding a copy of the event-handling function to every child).
The .live() method goes a step beyond that and declares an event for every element matching its selector. However, the implementation of the .live() method is resource-consuming: it binds an event handler to the document root, so it’s involved every time the specified event occurs anywhere in the document.