There were some false reports a couple of weeks ago that a Zune client would be coming to the Mac soon. I don't think that will happen anytime soon, but that doesn't mean you won't be able to sync your new Windows Phone with your Mac. Similar to the way DoubleTwist works with Android and Nokia Media Transfer works with Symbian, you can use the beta Windows Phone 7 Connector to sync music, video, photos, and podcasts from iTunes and iPhone to your Windows Phone 7 device. I personally connect via both the Zune PC desktop software and this WP7 Connector utility at this time.
I primarily use a Mac for writing and even though I can boot into Windows I do not do this often. It is more convenient to just sync over podcasts and photos I gather in iTunes and iPhoto. You simply connect your Windows Phone, click Enable Sync, and then customize your sync options. Sync options include:
You can rename your device, delete all content, ignore the device, and check to sync metadata music information from the Zune service.
You then go over to the left side and click on each media type to define what content you want synced between the Mac and your Windows Phone 7 device. Of course, DRM protected content cannot be synced.
There is an option to browse the device from the left list as well so you can see what is loaded on the device and even select to delete items as needed for space considerations. The software is very easy to use and seems to work well, even in early beta form.