I checked in a psd that is the beginings of the default skin. It's in the design folder in the svn repo. Feel free to check it out and work on it. I'm planning on adding xml based skin descriptors to load the skins dynamically at run time.
I finally figured out how to wire up XCode to my svn repo here so you should be seeing code updates being checked in far more often. I've been working on the control base classes and the default skin. If anyone is looking to get thier feet wet implimenting carbon controls I would love the help. I can point you in the right direction if your new to it as I was more then alittle lost when I switched over from the windows sdk. Also any of you digital producers out there I would be really interested in hearing your 2 cents about features.