After upgrading to 10.4.4, my menu bar icons (clock, volume, displays, etc.) disappeared.
It turns out that if you have disabled Spotlight, when the updater replaces Search.bundle (located in System -> Library -> Core Services), it causes SystemUIServer (which controls the menu bar, among other things) to crash.
To fix the problem and get your menu bar icons back, just delete Search.bundle and restart.
[robg adds: We've noted similar issues when upgrading modified systems in the past, and it speaks strongly to the need to upgrade a 'standard' system. In my case, I have a simple note in Stickies listing the handful of non-standard things I've done to my machine. I also have a folder containing the original versions of modified files, and I put everything back to normal before upgrading.
I then reboot on the 'restored' machine, so that the original system is once again active prior to the upgrade. It's a bit of work, but I've never had an issue with a system update...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060112133143484