Just read this on Dave Hyattā€˜s Blog:

XSLT

Safari 1.3 on Panther now supports XSLT. 10.3.9 includes libxslt, and Safari uses this excellent library to handle XSLT processing instructions it encounters in Web pages.

html Editing

Safari 1.3 supports html editing, both at the Objective-C WebKit API level and usingcontenteditable and designMode in a Web page. The new Mail app in Tiger uses WebKit for message composition. You can write apps that make use of WebKit's editing technology and deploy them on Panther and Tiger.

I mentioned those 2 features before here and here. Very nice, that Apple decided to make them available also to OS X 10.3.

I personally don't use Safari a lot these days anymore, but some clients of us do, so this is a nice addition.