Last time I looked, it seemed to be pretty detached from the "real" demoscene. While there are quite a few Macs on parties, 99% of them belong to graphic artists (not too surprising, is it?)
Mac Compos are only held on the biggest parties (Assembly for example), which are sadly polluted by gamers. Most demos are just ports from the PC anyway and the good stuff never makes it to the Mac. Oh well, I hope this will change someday.