Says EA rep:
To the millions of SimCity fans out there, we’ve been listening and can proudly say that your calls have been answered. SimCity has a long legacy on the Mac and the team at Maxis is ensuring that it will be the deepest, richest and most accessible SimCity game yet.
So that’s good. On the downside, it will likely require an always-on internet connection to play (because that worked out so well for Blizzard, obviously).
UPDATE: Looks like the beta is for Windows only, and in any case the signup form is bugged.