Most Web page layouts rely on design patterns created for laptop and desktop computers equipped with a mouse and keyboard. As the variety of devices being used to access the Web has grown, these patterns haven’t been keeping up. Designing for today’s Web means considering single-handed thumb use on smartphones, two handed touch interactions on tablets, mouse and keyboard input on traditional PCs, hybrid devices, and more. Web layouts have to evolve to support this new reality. - Luke W., lukew.com
I love me some LukeW and while looking over stats, I found something interesting. From the limited sources I could find, users still prefer landscape.
Stolen From Appleinsider who probably stole this from somewhere.
Its too easy to assume mobile users will be surfing portrait and might be the majority. So next app, (especially iPad make it function both ways)