As much as I like the idea of supporting our Mac-challenged friends, I think the real benefit of a PC client would be the addition of new bodies, and hopefully, ideas, to the game.
The current number of players is getting dangerously close to the "it's not fun to play 'cause I can't get a good group together" stage. With the addition of a PC client, and the agressive pricing point ($6.66/mo
for the year contract), we should see a large influx of players.
The only downside I see is that the influx will be PC users...