I think it's a neat idea. I got scared at first. When I was linked from CNN, they had implied that apple planned to do away with OSX completely in favor of iOS, should this come to fruition.
When I read the article about it switching between the two, depending on the position of the monitor, I thought it was kind of neat.
Not too sure about smudging up my main monitor, however. Personally, I don't think I have a whole lot of use for iOS on a full size computer, and would much rather just see apps available on OSX, but I see where they're going with the idea, and I'm not against it either. Like I said, it's pretty neat, anyway.