I just updated to 10.5.4 today and now I cannot enable Fast User Switching. I've rebooted several times. I have no username showing in the menu bar. When I try to turn it on in System Preferences, I can check the box, but the View As: dropdown never enables so I can change it from Name to something else. And then, when I close System Preferences and open it up again, it's unchecked. Any ideas? Also, another odd thing, I have an NAS, and when I first log in, I get a request to log into the NAS. The default username is NOT the one I logged in on, but a different user (that doesn't require a password). It's easy enough to change the user name and enter the password so the network drives mount, but even though I checked the box to remember the login info in my keychain, OS X asks me to enter it all again every time I reboot. Thanks all!