How similar are the US and UK versions of the Office?

I saw a repeat of 60 minutes last night, where they were showcasing Ricky Gervais. A few of the things he does on the UK office are emulated in the Americanized version. I don't care to watch the UK version, since I can barely understand what they're saying -- so, I'm wondering, for those who have watched both -- how similar are the two?