[iandwk]

I know from laying tile that it's about as easy to do it one way as the other. I've heard of installers charging more for laying it diagonally, but there are about the same amount of cuts either way and the cuts are no more or less difficult either way. Other than that, it becomes a matter of personal preference.

Rounded sheetrock corners I would assume are useful in the sense that you aren't constantly chipping the mud from the sharp corners. I'm sure others know more about that, though.