Where I live it's really common. We sometimes joke at work if they drug tested our large organization they'd have to let go of most of the employees. It's about as socially acceptable as drinking, which I think is fine considering alcoholism while legal is more damaging.

I started smoking a lot after a traumatic event and anxiety. I do worry that it effects motivation. Anxiety does also though. I don't have a lot of faith in the pharma industry. I think as one poster mentioned, the head space of weed (versus pharmaceuticals, coffee, or other legal substances) maybe lends itself more to the arts than typical 9-5 office work. I think for some users who work for themselves it probably isn't that bad, especially if they have another disorder it is treating (like anxiety or adhd). I've known several people who for example had bad reactions to prescribed adhd medication, and felt weed was a better option for them with less negative side effects.

No two brains are the same, each person probably reacts differently. There is also major stigma with pot as a controlled substance that makes probably makes some research a bit bias.