P.S. -Oh, purists, you'll definitely love the fact that you can now (finally) turn off menu bar transparency. Score one for the team. (It's in the desktop and screen saver system pref pane.)
P.P.S. -It would appear there's also a second update, the Leopard Graphics Update (about 50MB) which comes through once you've installed 10.5.2. No word on what that one does yet. Thanks, amidamaruflame.
Some of those fixes:
AirPort: Improves connection reliability and stability, more.
Dashboard: Widget performance improvements (as in Dictionary), more.
Dock: Updates Stacks with a list view and folder view options, and an updated background for grid view.
Mail: Improved data detector accuracy, hurts Growl users in disabling GrowlMail version 1.1.2 or earlier (to avoid issues), but also has tons of other fixes.
RAW support: Now supports more RAW formats / cameras (presumably more on Apple's site).
Time Machine: Adds a menu bar option for accessing Time Machine features (the menu extra can be enabled in Time Machine preferences), among other things.