mine was super loose too when I bought it and I didn't catch it until a week later. I also ran across a youtube video of a later model (a believe it was a gen2 ) that had been driving around with a broken tensioner and the belt was still being driven but off time by a tooth or two. The owner complained that the acceleration felt sluggish but otherwise it drove down the road and sounded fine... not sure those anecdotes constitute this being common but from my extremely limited experience, that makes at least three of them that I know about.
I'm definitely getting another non-interference engine to replace the original with when I do it. (not that I PLAN on being lazy - but ...you know.....ha)