From Apple's update notes in the knowledgebase:
The following improvements apply to both Intel- and PowerPC-based Macs unless otherwise noted:
.Mac
* Improves automatic iDisk syncing for customers whose .Mac username contains a period (.).
* Improves overall .Mac Sync performance.
* Addresses an issue with automatic and periodic syncing as set in the .Mac System Preferences panel.
* Reduces .Mac Sync timeouts when syncing large data sets.
* Prevents large amounts of Address Book data from being changed without authorization.
* Addresses an issue which could result in properly unregistering a computer.
* Addresses issues related to syncing a large number of changes to .Mac
* Prevents third-party syncing applications from presenting an extraneous initial sync alert.
Bluetooth
* Addresses a wake-from-sleep issue for Kensington PilotMouse Mini Bluetooth devices when used with a MacBook.
* Resolves issues in which Bluetooth-based devices might not respond after sleep on some computers.
iChat, iCal, and iSync
* Resolves an issue in which iCal reminders may appear off to the side of the screen.
* Resolves an issues in which some events added to particular dates may not display correctly.
* Event notes are now synced between iCal and Nokia N70 phones.
* Adds iSync support for more devices.
* Includes iChat support for USB Video Class webcams.
Networking and modem
* Addresses a permissions issue when copying a file with extended attributes from an AFP share of an Xsan volume, via the Finder.
* Resolves an issue when using kerberos authentication with Active Directory if the user is a member of many groups.
* Resolves performance issues with Intel-based iMacs that could occur when determining high-speed network switches.
* Improves reliability when faxing in France or Belgium via an external Apple USB Modem.
* Adds support for WPA2 encryption in Network Diagnostics.
* Addresses an issue with automatic AirPort connections that use different authentication methods.
* Addresses an issue in which Network Preferences may unexpectedly quit after disconnecting a network-aware USB device while Network Preferences is open.
* Addresses an issue with iMac's maintaining manual duplex settings.
* Internal Apple modem drivers now offer the same robustness as external Apple modem drivers.
* External USB modems now report DLE-d for busy tone detection.
* Adds modem support for Russia.
* Fax receiving now works when the country code is set to France.
* Resolves an issue with dialing a modem in pulse mode to an ISP.
* Resolves an issue in the Open dialog when browsing AFP volumes within applications using Rosetta.
* Resolves a printing issue that could occur with applications using Rosetta, while logged in as Active Directory User that has an SMB home directory.
Printing
* Resolves a printing issue with applications using Rosetta while logged in as an Active Directory User with SMB home directory.
* Resolves an issue in which temporary files might use excessive disk space when printing to some third-party printers.
Aperture
For information on the benefits this update includes for Aperture, see this article.
Third-party
* Resolves issues for these third-party applications that use Rosetta: LEGO StarWars, Adobe InDesign, H&R Block TaxCut, Big Business' Big Business 5.1.0.
* Resolves an issue in which Adobe Arno Pro Italics fonts might not install in Font Book.
* Resolves an issue for Microsoft Word in which OpenType Fonts may not display correctly; this update also addresses OpenType font issues using Word 2004.
Other
* Improves the reliability of OpenGL-accelerated graphics in Blizzard's World of Warcraft.
* Improves the reliability of OpenGL-based applications on Mac Pro computer with Nvidia graphics cards.
* Includes updated security certificates.
* Includes the Daylight Savings Time Update (released February 15, 2007) which contains the latest worldwide time zone and Daylight Saving Time (DST) rules as of January 8, 2007.
* Resolves a toggling issue when zooming using the Command-Alt-8 key combination (Universal Access).
* Resolves an issue in which some USB printers may stop printing in Classic.
* Addresses an issue in Classic in which an iMac G5's built-in iSight camera might stop responding.
* Improves validation of disk images.
* Includes improved support for USB devices in Classic.
* Improves support for files with ".ac3", ".m2v", and ".m4v" filename extensions.
* Improves performance when transferring from a P2 USB reader in the Finder.
* Resolves an issue in which DVD player might not play a track that's longer than 3 hours.
* Addresses a display issue that could occur in X11.app running in 256-color mode on an Intel-based Mac.
* Addresses EAP-FAST in PAC mode issue in a TLS session.
* Addresses an issue in which incorrect encoding could be used for the files created by the “New Text File” Automator action on Intel-based Macs.
* Includes recent Apple security updates.