Working my way through SICP and got to the point where I felt comfortable contributing to the answers.

I'm currently using DrRacket (formerly DrScheme) as my learning platform which is making some of the coding a bit tricky. I'm trying to stick with the default #lang racket which seems closer to r6rs than r5rs. The biggest issue so far is dealing with the fact that racket pairs are immutable. Adding (require racket/mpair) and lots of whacking m's in front of pair operations solves most of the issues.