iGoogle uses yui (Yahoo User Interface Library)
Funny, I would imagine that they have developed an in house JavaScript library by now but this is great, using a well maintained and good library is a great programming practice.
You can check it out here:
http://www.google.com/ig
(Right click and view the source)
Yes, I have to see the source code for everything I can find 
I personally can’t imagine living without jQuery, I used yui for a long time but jQuery is a beautiful piece of engineering.
yui is still great and has so many components but it’s not my type, I’m lazy 
Archived under JavaScript, jQuery, yui Comments
