That's awesome that you've introduced it to that many people. I haven't really been able to get people interested more than tangentially. Good for you.
>Does Arc 3.1 run properly though on MzScheme 372 or does it need to run on Racket?
I haven't tried running it on MzScheme 372; once I could just use the most recent version of Racket, I decided to just do that. It seems easier than staying on an old version.