I thought this was a great quote -- 
"If you want to play around with something that is in the spirit of the old MIT and Xerox Lisp machines, I recommend http://www.squeak.org/ (not a comprehensive computing environment like Unix or WinXP but fully understandable within a human lifetime, unlike Unix or WinXP, and therefore easy to modify/extend)."

http://philip.greenspun.com/bboard/q-and-a-fetch-msg?msg_id=000tdN&topic_id=Ask%20Philip&topic=