I have been programming for many years in languages such as Assembler,C, C++ and Python. I found I had not many difficulties with getting the concepts of Assembler and C, but concerning C++ and Python there were many things in these languges which I was not able to use effectively, since I did not understand the concepts. That is where Simply Scheme is such a great book. It explains quickly and easily ideas such as recursion, vectors, trees and general symbolic programming. It also helps with terminology, giving names to things I had been doing for years, but had not defined.
I would suggest this book as a great step to those who can doing many things in lower level languages, but want to extend their effeciency. I do not think I would ever use the Scheme language as such, but I will certainly use what I have learned in this book for my programming.