According to this search, SimCity 4 is targeted to come to the Mac!
I have actually been considering getting a PC recently in order to have a machine to play Sims Online and SimCity 4 on. Sue me, I like to build things. So when I can't actually be in a city of interesting size, it's nice to go into one of my creation and hang out in certain simulated neighborhoods. People watching in SimCity 3000 was curiously fun, and now in SimCity 4 you can actually move your Sims characters into the city. You can't follow the minute details of their lives like you can in The Sims, but you can use them for feedback, or watch them on their daily commute and get a feel for how bad the congestion really feels and is affecting their mood.