Update 5/17/2008: This issue has since been fixed with the release of the Virtual Earth v6.1 release. There is still a small issue related to the CalendarExtender and Virtual Earth that only occurs in Safari. You can read more about it here.
I do alot of development with ASP.NET AJAX and Virtual Earth, and each of them work fine by themselves in Safari 3 on Windows. However, if you use them both on the same page, it will cause ASP.NET AJAX to break and stop working in Safari.
I don't have a Mac, so keep in mind that I haven't tested this in Safari on the Mac. I've only verified this issue in Safari 3 on Windows.
This is a real issue for me, since I can not add Safari support to my Web.Maps.VE product because of this issue. I know it's probably an issue with Safari, since everything works perfect in IE and Firefox, but I hope it gets fixed soon.