Quick Link: Forget addEvent, use Yahoo!'s Event
Dustin Diaz goes in depth on Yahoo!'s event handling. The biggest plus is the ability to attach a handler to an object before it exists in the DOM. I suspect we'll see something like this in Prototype soon enough.
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I've patched Prototype to include this functionality. Sam says that he digs it and will be adding it to the distribution soon. Ticket is here: http://dev.rubyonrails.org/ticket/3940
You the man Justin. :)
Justin, That's awesome man. Good to hear Prototype is going this route. You guys rock!