I ran into a problem Monday night where I couldn’t log into my Mac. I got a “SystemUIServer unexpectedly quit” message. After messing around on Tuesday evening, including deleting my ~/Libraries/Preferences/com.apple.systemuiserver.plist file (as recommended on a troubleshooting website) I gave up and reinstalled the OS. Fortunately it went well with no lost data.
My best guess is that Netbeans caused the problem. I had started an automatic upgrade that requires a restart of the machine while Netbeans was open (actually opening). Most applications on the Mac allow the shutdown command to shut themselves down, but Netbeans, instead, cancels the shutdown command. I suspect that somehow the cancelled shutdown got the upgrade into an unusable state.