Public opinion may be changing, but I don't think we have really carefully examined how this will play out in every day life (what Skip mentioned). For example, I doubt most people want a pothead piloting their plane, driving their city bus, taxi, school bus, etc. The easy answer is to treat it like alcohol, but I'm not sure how easy or difficult it will be to enforce.
Regarding the workplace, employers should be able to regulate it just like they do any other drug, including alcohol.