Just read an interesting article about the use of a proprietary Lisp variant in the game "Jak and Daxter: The Precursor Legacy":
http://www.gamasutra.com/features/20020710/white_01.htm
Covers the pros and cons of using Lisp. Among the cons:
"A single programmer (who could easily be one of the top ten Lisp programmers in the world) wrote GOAL. While he called his Lisp techniques and programming practices 'revolutionary,' others referred to them as 'code encryption,' since only he could understand them."
Amusing :)
Vish