The OS looks the same, pretty much. New features obviously look different, dashboard, spotlight, etc.
http://www.apple.com/macosx/
I was using the Tiger build from WWDC a year ago. Very nice, a little buggy, and automater wasn't near finished. Spotlight is amazing, Safari 2.0 is amazing, runs faster, and of course, the dashboard is the shiznit if you download some of the widgets over at
www.dashboardwidgets.com .