The only time I use it in landscape is watching movies/videos etc, and games or any apps that basically require it. Otherwise it's portrait, probably an 80/20 split of time.
I imagine when multi-tasking kicks in for me I'll prefer portrait even more, as I've found using the home button rather tedious when I am in landscape.
Mike
For me, it depends on the situation. If I'm reading, it's in portrait; if I'm watching video, it's in landscape. Also, when I write down notes (penultimate), it's in portrait. When I use my laptop tray and case with stand, it's used in landscape. That's the beauty of it, you can use it either way.