Slightly off topic but I do not want to post another Ask HN question: what implementation of Scheme would you guys recommend/use? Working smoothly would emacs would be appreciated
MIT Scheme (http://www.gnu.org/software/mit-scheme/) includes a version of EMACS that runs in the same Scheme address space and is therefore well integrated. It's entirely sufficient for doing SICP.
Further update: 6.184 is being taught by the best of the last batch of 6.001 TAs, some of whom taught it 6 or 7 times. Their recommendation of Racket is therefore likely to be well informed.