Scheme is not my first language and I am still greatful for it. I am self learning SICP for past 3 years (after working 15+ years in non-lisp languages). Though still in chapter 2, it has cleared up and simplified my thinking about programming. I no longer consider bottoms up approach to be sin. Understanding new functional language specs becomes a breeze and it 'just clicks'. Though I am yet to understand why Clojure could not implement tail recursion without the 'recur' keyword.