And the physics of it were totally consistent throughout. Granted, they never mentioned much, but the things they did mention were fixed and unchanging.
I was a huge QL fan, but... no.
At first nobody could see Sam's true form. Then children, the insane, animals, guys with funny hats, and basically whatever the plot required could see him.
And then there's the thing with his ability to leap "within his own lifetime". They made a huge deal out of that, repeating it in the opening sequence for almost every episode. But then in the last season they broke down and started doing "celebrity leaps". Sam is Elvis! Sam is Marilyn Monroe's chauffer! Sam is Lee Harvey Oswald! Yeesh.