Implementation is where theory and practice collide in a conflict! In GNU tradition, guile (a Scheme) is widely available. Personally, I've found newLisp (http://www.newlisp.org/) to be small, fast, portable across all main platforms, good if you want to deploy web-apps, not so good if you want to write full-featured GUI apps.

As for the Linux comparison, once you really know (i.e. can use command line, the shells, awk, grep, sed, etc) one Linux distro, you can work your way through the others and even AIX, the various BSDs, HPUX, Mac OS/X and Solaris.