10.5.4 was realeased today and not major changes that the eye can see but here is what happened with 10.5.4 :

• Includes recent Apple security updates.
• Resolves an issue with saving and reopening Adobe Creative Suite 3 files on a remote server.
• Includes additional RAW image support for several cameras.
• Addresses an issue that may result in a partially installed X11 application.
• Improves L2TP VPN client reliability.

AirPort

• Addresses AirPort reliability issues with 5GHz networks.
• Addresses AirPort issues that may result in slower performance in Logic Studio or MainStage.

iCal

• Improves overall iCal reliability for meeting requests, cancellation notices, delegation, and syncing with iPhone.
• Resolves an issue that prevents deleting an iCal event without notifying the creator.
• Addresses an issue in which events in all calendars affect availability. A checkbox now enables information-only calendars to be transparent from free/busy lookups.
• Resolves a UI issue preventing delegated calendars from showing up as a separate window.
• Addresses an issue with copying and pasting attendees from one event to another.
• Resolves an issue in which iCal may not delete events after a specified time interval, even when set to do so in iCal preferences.
• Addresses an issue in which To Dos cannot be marked private.

Safari

• Addresses a potential performance issue when loading secure web pages.
• Resolves issues that may be encountered when accessing secure web pages with client certificates that reside on a smart card.

Spaces and Exposé

• Addresses an issue in which switching from a space with a Finder window keeps the Finder as the active application instead of the application residing in the destination space.
• Fixes an issue in which dragging an application from the list of application assignments in Spaces System Preferences does not assign the application to the desired space.
• Resolves an Exposé issue that may result in only a subset of windows being shown.