I meet mac user players fairly often. One way I spot them is when they ask on newbie why greet isn't working. In our mud we use greet
But as far as admins, owners, gods etc I don't think I have actually run into any at all. I found it useful being on a mac when we were developing the code for our mud, I was able to make sure it was all working as we wanted it to from the mac point of view. Had to run a few different mac clients to make sure all the ansi was showing up correctly and the maps were displaying right. Maybe that kind of thing is not so important on a code base that has been around for a while.
So if you are a builder or whatever, what kind of problems have you had? I used to be an imm on a diku mud and they had no OLC, and I couldn't track down any kind of building client that would run on a mac. So I was basically taking the code for an existing area, reading through it all and building my area in a text file copying the code I already had. sheesh!.. never did get that area finished either *grin*