As usual, backup to another drive before running the update (if possible). Always repair your permissions and startup drive using Disk Utility or other software like DiskWarrior before, and again after any major installations/updates. Never update in the middle of a project.
Please post how it is working for you and what applications you've tried it with so far.
10.4.5 Update is recommended for all users and includes general operating system fixes, as well as specific fixes for the following applications and technologies:
-Address Book, AppleScript, Automator, Dictionary and Font Book
-iCal, iChat, DVD Player, Mail, Preview, Safari and Stickies
-Disk Utility, Keychain Access, Migration Assistant, Software Update
-usability of Dashboard and widgets
-viewing of QuickTime streaming media behind a firewall
-time zone and daylight savings for 2006 and 2007
-RAW camera support, including updated ATI and NVIDIA graphics drivers
-sharing using AFP, SMB/CIFS, NFS and FTP file sharing protocols
-reliable access to Open Directory, LDAP and Active Directory services
-VPN connections to Cisco servers when using NAT
-AirPort and Bluetooth wireless connectivity
-compatibility with third party applications and devices
-previous Mac OS X updates and standalone security updates
So far seems to be working fine. A few "unexpected quits," but no more than with the previous version.
Final Cut Pro 5.x
DVD Studio Pro 4
I-Tunes (latest version)
Photo Shop CS2
Sorenson Squeeze 4.1
I've had no problems so far at all, but more testing with various application will be needed before I give it my blessing. I believe some of the utility applications are not working correctly (non-apple) and will need to be updated. These updates usually happen very quickly though.