1) In places where pot's legal now, are people being released from prison and getting their criminal records erased? Haven't heard anything about that. Doesn't seem right to keep someone in jail for something that isn't a crime anymore, but figuring out who to let go - and who to keep locked up (for various reasons) - sounds like a huge legal mess.
2) What about the DEA? The agents I've known absolutely believed they were doing God's work. I doubt they'll just let go. If they don't go after pot anymore, then Washington might want to seriously reduce their operating budget - and I'm sure the DEA will fight tooth & nail to keep every penny. Things could get ugly.