Apple has released the Mac OS X 10.5.2 Leopard updates. The 180MB download is now available via Software Update, and a restart is required after installation:
The 10.5.2 Update is recommended for all users running Mac OS X Leopard and includes general operating system fixes that enhance the stability, compatibility and security of your Mac.

For detailed information on this update, please visit this website: http://docs.info.apple.com/article.html?artnum=307109.
For detailed information on security updates, please visit this website: http://docs.info.apple.com/article.html?artnum=61798.

A number of improvements are detailed, but some highlights are listed here:

- Airport: Improves connection reliability and stability
- Back to my Mac: Adds support for more third-party routers, as detailed in this article.
- Dock: Updates Stacks with a List view option, a Folder view option, 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.
- Desktop: Adjusts menus to be slightly-less translucent overall.
- iSync: Adds support for Samsung D600E and D900i phones.
- RAW Image: Adds RAW image support for several cameras, as detailed in this article.
- Safari: Addresses issues with Safari reliably resolving certain domains.
- Time Machine: Adds a menu bar option for accessing Time Machine features (the menu extra can be enabled in Time Machine preferences).
- Time Machine: Improves backup reliability when computer name contains slash or non-ASCII characters.
- Time Machine: Addresses issues in which some external drives are not recognized by Time Machine.