There is a site for Mathematica which seems very active. Maple does have Mapleprimes.com which is a whole mix of stuff and not so active. I'd think that both systems get wide use.
I have my own reasons for preferring Maple (not trying to start anything...) and use it enthusiastically if idiosyncratically. A reasonable response might be: OK make up 20 seed questions and start it! but maybe there is history or better informed people who'd join in etc.