I haven't had the same experience as jaredmcateer. I often find myself more focused when I'm high - it's easier to achieve that flow state and to think creatively. Cannabis can be very helpful for seeing big ideas and thinking in modes that are different from your everyday way of thinking.

That being said, I've only been high for personal programming projects, I wouldn't be likely to smoke before an interview.

It's not like it is some foreign psychedelic experience, you're just slower and less focused. With experience that's probably mitigated as well. I suspect if weed didn't affect my motivation so much it would be fine but only thing I want to do when under its influence is sit down watch some comedy and eat junk food, until I fall asleep.

It varies from person to person, also varies with the amount smoked.

If I smoke any amount I just zone out and get paranoid, while I have friends who get high and do their discrete math homework.