MU is a lie.

Death Note end spoilers

Or if not a lie a very well-crafted bit of misdirection.
*checks 1*.... nope, just an outright lie. (I thought perhaps Ryuk had said something like "And those who have used the Note have a different fate waiting for them. Don't think that a human who has used the Death Note can go to heaven or hell." Then when Light's like "Well 'cause they don't exist right? 8)" it would still be totally legit to answer, "Nope, you're right, they don't" while still not answering the question of "Do Note users go to MU?". If it was a special case. But it's not indicated that it's a special case.)
It's a lie! According to an interview. Littlejohn-san says that according to an interview Death Note users become shinigami DATTE MINNA SOU OMOTTA JA NAI DESU KA. Ack. It's a little frustrating and yet so... relieving because everyone thought he'd become a shinigami. ...Everyone! >3<

So I've actually wondered for quite a while if MU was false anyway--it does after all seem really, really tacked on. With the whole, "At this last moment let's flash back to Light's doe-eyed days to a conversation that suddenly exists and yet existed the whole time 8D" thing. And knowing that the editors or someone demanded that there be punishment for Light. Becoming a shinigami isn't punishment. Innnnnn fact unless he loses his memory we are worse off than before. (Free eyes yaaaaa--uh-oh.) Which leads to an incredibly interesting question about the morality of that--someone who really is a shinigami, killing..... but..., it says the murders stopped.......? Hmn. Maybe he does lose his memory. Or his interest? He's all like, "I'm a human doing this for humans."
Well whatever.
I like being right.