I really did not notice much difference on my machine (DP 800). I think most "improvements" were for stability, security, and are behind the scenes. A couple of exceptions (though I suppose there are more), the Keyboard & Mouse and now united in the System Preferences, and in Safari, the minimum size font is now ~9 point (I'm guessing), e.g., sites with microscopic fonts are once again easy reading for these old eyes.
FWIW, The new TinkerTool 3.01 (10.3 compatible) allows one to once again set Safari's minimum font to any size that warms your heart. There are also many other nice improvements (IMNHO).
Harv