This just in-- Silverlight 4 works very well on a Mac with Safari!
I had to share a screenshot of our IntelliGantt Web Part talking to SharePoint and running on an Apple Mac:
Looks pretty good! Also, please notice that our web part is running inside of WSS 3.0 in this picture. I will post 'How-Tos' in the next couple days on how to site the control in SharePoint 2010, SharePoint Foundation 2010, MOSS 2007 and WSS 3.0.