Apple releases Mac OS X 10.5.5 Combo Update

Apple has released Mac OS X 10.5.5, a recommended update for all users of Mac OS X 10.5.x. A deatailed list of the update can be found here. IMHO, you should update via download the combo standalone updater rather then software update.

General
• Includes recent Apple security updates. Mac OS X client is now doing the required DNS  address port randomization.
• Addresses stability issues with video playback, processor core idling, and remote disc sharing  for MacBook Air.
• Addresses an issue in which some Macs could unexpectedly power on at the same time each day.
• Resolves a stability issue in TextEdit that could be found when accessing the color palette.
• Improves Spotlight indexing performance.
• Fixes an issue in which contacts might not sync properly with PalmOS-based devices.
• Improves iPhone sync reliability with iCal and Address Book.
• Includes improvements to Active Directory (see this article for more information).
• Improves Speech Dictionary.
• Fixes Kerberos authentication issues for Mac OS X 10.5 clients that connect to certain Samba  servers, such as Mac OS X Server version 10.4.
• Includes extensive graphics enhancements.

Address Book
• Addresses stability issues that may occur when creating a Smart Group.
• Resolves a printing issue with address cards containing information that spans more than one page.

Disk Utility and Directory Utility
• Improves reliability when rebuilding a software mirror RAID volume in Disk Utility.
• Improves reliability of server status displayed in Directory Utility.

iCal
• Updates iCal to more accurately handle repeating events.
• Improves performance when choosing meeting attendees.
• Resolves an issue in which the "Refresh All" option may be dimmed ("grayed out") in the  contextual menu for certain calendars.
• Fixes issues with read-only calendars.
• Addresses an issue that prevents an invitee from moving an event to a different calendar.
• Resolves an issue with syncing published calendars.

Mail
• Addresses performance issues related to displaying IMAP messages.
• Resolves an issue with SMTP settings for AIM, Compuserve, Hanmail, Yahoo!, and Time    Warner Road Runner email accounts.
• Addresses stability issues that may occur when dragging a file to the Mail icon in the Dock.
• Addresses an issue with the "Organized by Thread" view in which the date does not appear        when the thread is collapsed.
• Resolves an issue in which RSS feeds could temporarily disappear from the sidebar.
• Improves Mail robustness when sending messages.
• Improves reliability when saving drafts that have attachments.

MobileMe
• Improves overall sync reliability.
• Improves Back to My Mac reliability.

Time Machine
• Improves Time Machine reliability with Time Capsule.
• Addresses performance issues that may affect initial and in-progress backups.
• Fixes an issue in which an incorrect alert message could appear stating that a backup volume     does not have enough free space.
•Time Machine can now back up iPhone backups that are on your Mac, as well as other items in (~/Library/Application Support).