Apple - How do I permanently disable Notification Center in Mavericks?

If you start Terminal, enter

sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool False

and restart, this did the trick for me in Mavericks.

Just unloading the plist still works for me:

launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist

If the plist is not loaded, sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool False should have no effect.