Perhaps the most important insight to be gained from this article is Abelson's statement that "a lot of times you crud up a program to make it finally work and do all of the things that you need it to do, so there’s a lot of extraneous stuff around there that isn’t the core idea." There is an old blog entry by Joel Spolski that elaborates on this phenomenon:

http://www.joelonsoftware.com/articles/fog0000000069.html