As part of my team's work we bought a Mac for testing. Setting aside how cute that little box is and how interesting it's been to get it to work on the Microsoft network (bone up on your IPSEC, please), we've been trying to get Safari to work and have found that, unlike Firefox and IE, Safari often behaves very strangely. Some querying around among people who know and a conversation with the principal architect at another company told me that many people seem to have problems making their AJAX sites work with Safari. A further query found that http://webkit.org is evidently the development ground for what becomes Safari, and poking around on that site and found that http://webkit.org/projects/compat/hitlist.html had a variety of AJAX-related issues (live.com is heavily AJAX-based) as the biggest compatibility hit list items, along with a set of bugs like http://bugzilla.opendarwin.org/show_bug.cgi?id=6519 that indicated that these were P2 bugs of severity “major.” Granted, they're not P1 showstopper bugs, but it's very cool to be able to see the work that's going on.