Well, thanks to some underlying work built-into Jellybean, this is entirely possible and is already there so if you’re running multiple users under the same device, it’s already there! (well, you need root at the moment)
To get it working, simply run in a terminal (over adb shell or Terminal Emulator):
su pm create-user username
And as if by magic, you should be able to see this in the Power menu:
However, your new user has limited power over your device, however we can expect some more options in the future, as it’s only natural to allow this to happen.
If you want to read up more, check out the full post on XDA Developers