The Mac OS X 10.5.3 Update is recommended for Mac OS X 10.5, 10.5.1, and 10.5.2 Leopard. It includes general operating system improvements that enhance the stability, compatibility, and security of your Mac.
For detailed information on this update, please visit this website: http://support.apple.com/kb/HT1141.
For detailed information on security updates, please visit this website: http://support.apple.com/kb/HT1222.
If you are nerd and enjoy reading technical documents then check out all of the bug fixes in 10.5.3 here. So here is the Cliff Notes version for the rest of us:
Some highlights include:
* Address book update to synchronize with Google, Yahoo, .Mac and Exchange.
* Includes fixes for Time Machine compatibility with Time Capsule.
* Improves 802.1X (Wifi) behavior and reliability and when using Time Machine.
* Improves Active Directory binding and login.
* Eliminates a delay when logging in as an Active Directory user in a .local domain.
* Fixes reliability issues with iCal syncing.
* Fixes an issue in which certain attached hard drives may not show up in the Finder.