Well today I am learning Prototype and Scriptaculous.  Up until now I’ve been using my own home grown Javascript library, but I’ve decided it is time to see what else is out there.  Clearly anything open source will have a lot more testing, features, and support.  I decided to start with this library largely because of the book Prototype & Scriptaculous in Action by David Crane, Bear Bibeault, and Tom Locke.  It was released at the perfect time for me to use it.  After I feel comfortable with these libraries I think I’ll move on and try YUI next.