from Mac Rumors

The 10.4.3 Update delivers overall improved reliability and compatibility for Mac OS X v10.4 and is recommended for all users.

It includes fixes for:

- AFP, SMB/CIFS, NFS and FTP network file services
- AirPort and Bluetooth wireless access
- Core Graphics, Core Audio, Core Image, and RAW camera support
- disc recording when creating and burning media
- .Mac sync services
- Spotlight indexing and searching
- Dashboard widgets: Dictionary, Flight Tracker, Stickies, and Unit Converter
- Address Book, AppleScript, Automator, Dictionary, Font Book, iCal, iSync, Mail, and Safari applications
- Disk Utility, Keychain Access, Migration Assistant, and Software Update
- compatibility with third party applications and devices
- previous standalone security updates

For detailed information on this Update, please visit this website: http://www.info.apple.com/kbnum/n301984

For detailed information on Security Updates, please visit this website: http://www.info.apple.com/kbnum/n61798

However there are some rumors going around about it.. :)

from xlr8yourmac.com

Initial reports on 10.4.3 Update breaking EyeHome, Safari Enhancer, cracked Front Row – Just a FYI/warning to readers that I’ve gotten a mail that EyeHome (v1.6 ), Safari Enhancer 3.0 and some rumor site “widgets” were broken by the 10.4.3 update. (I avoid “Widgets” like the plague personally…) I suggested he write El Gato about the EyeHome software problem (if this is common hopefully they’re working on an update.)
Also a reader with a G5 mac running a cracked version of Front Row said it no longer runs after the 10.4.3 update.
If any readers find 10.4.3 improves performance, fixes or breaks anything, let me know. (As mentioned earlier in the 10.4.3 update item below especially interested in DL drive owner reports on 10.4.3/iDVD 5.0.x dual layer project support – without the previous hack and with no patchburn profile installed.)