Common Lisp for Schemers

What's the best way for a Schemer to learn Common Lisp? It seems like Scheme itself is a more beautiful language, but the efforts made by many implementations to make Scheme useful "in the real world" lead to a big ball of mud™. Does Common Lisp avoid this problem? Should I keep trying to learn different Scheme implementations instead until I find something I like?

>>13
Read Strachey (1967) you uneducated fuck. I know exactly what referential transparency is and why macros break it.
Here is a good discussion to get you started: http://stackoverflow.com/questions/210835/what-is-referential-transparency