Panther's Fast User Switching is a great feature, but it's flawed by a glaringly bad UI design: the menu displays your long user name, taking up a huge amount of valuable right-hand-side menu bar real estate. Enter WinSwitch, which came out a couple of days ago and has already been updated to version 1.2.
This is the best replacement for Apple's user menu yet. It allows you to show a narrow icon in the menu bar, or the custom picture of the current user; or for those so inclined, the short or long forms of the username. It faithfully replicates the rest of the functionality of Apple's version, while fixing a couple of bugs in their implementation and adding a shortcut to the Accounts pane in the System Preferences.
WinSwitch is free/donationware, comes with an easy-to-use installer, and is open source to boot. A must have for anyone who uses Fast User Switching. It seems Apple would be crazy not to roll this into the next major release of Mac OS X.
[robg adds: Remember my comment in the above LaunchBar iTunes hint about launchers, etc.? Here's an example of why I love Butler -- my fast user switching is now on a hot key that I created (cmd-ctrl-F) and it pops up under the cursor whenever I hit that key combo. Set up this way, it takes no menu space at all. WinSwitch, though, definitely does the job and is a nice advance over Apple's design if you're looking for a standalone solution.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040401125531776