The Mac OS X 10.5.2 Update is recommended for all users running Mac OS X 10.5 or 10.5.1 Leopard. It includes general operating system improvements that enhance the stability, compatibility, and security of your Mac.
This update delivers several improvements for both PowerPC- and Intel-based Macs (as well as improvements provided in the Mac OS X 10.5.1 update.)
As expected this update has a TON of fixes, including stuff in Active Directory, AirPort, BTMM, Dashboard, Dock, Finder, iCal, iChat, iSync, Mail, Preview, Safari, Time Machine, and more.
Here is the Brief info of the few fixes:
Active Directory: Addresses issues which could hinder or prevent binding Mac OS X 10.5.x clients to Active Directory domains.
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.
Desktop: Addresses legibility issues with the menu bar with an option to turn off transparency in Desktop & Screen Saver preferences.
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.
Networking: Addresses a hanging issue that may occur when connecting to an AFP network volume.
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.