A few things I’ve noticed:
Safari 3: Beautiful new Find command. SVG support. Send to Dashboard capability. Drag and drop tabs, including to new windows. Better standards support.
Firefox 3: Better appearance which (unfortunately) highlights that Firefox doesn’t act like a Mac application. Looks like you can move the window from title bar, tool bar or status bar, but only title bar actually works. But where does the title bar end? Nice new security screen, which was implemented in a way that breaks one click URL selection. Improved standards support. Drag and drop tabs can’t be dragged to new window. But non-modal password prompt almost makes up for all its flaws.