Wow, that's a lot of votes for landscape! I really didn't think anyone used it in this way. Those with smartphones, when you go online do you turn it sideways too?
I use my iPhone portrait. With my iPad I find the keypad too small when it is in portrait and I also find it difficult to balance it on my lap when it is in portrait (one of my four year olds uses an iPad a lot and he uses it in landscape too).