I find this video incredibly interesting, thanks for posting.

One aspect of it is that some of these actors are so clearly wrong for the part. And it's not like they could have taken the role in a very different direction, because it's all based on a existing BBC show with established characters. (Adam Scott as Jim would have been great though)

But also, that they have had these (relatively) famous people audition is odd to me. One of the things I find so interesting in The Office US is that in the British version there's only four real characters involved, all the others are just window dressing and only get a few lines here and there. And that's why I thought that they hired these unknown actors in the US version (look up the resume of people like Angela Kinsey and Brian Baumgartner, they had done nothing until the Office), and then as the show progressed they got more and more to do, and they turned out to be pretty great at it.

But now in this video I see people like Eric Stonestreet reading for Kevin (already with a number of credits when this was casted), so I guess I was wrong and they were casting an ensemble cast.

Same here...one of the things I found interesting is the screen test of Brian Baumgartner as Kevin. He got the role but in the screen test he is playing the character very different then how he does on the show.