What people seem to be forgetting is that web pages are created for a certian pixel width. I use fbreader in portrait mode but would never use the browser in it - first, pages are designed to be scrollable vertically and not horizontally. Second, there is no screen that allows viewing pages in portrait mode without zooming. Third, even if we had screens that had a 800-1000pix vertical, the content would be microscopic. I understand the iPhone approach - you would be zooming no matter how you hold it, so then why not do it in portrait, but the advantage of the NIT-s is/was exactly that - see web pages in full width.

As for portait mode desktop browsing, the same applies there, too - it works if your vertical is big enough - try portrait surfing with a 1024x600 screen and you'll see what I mean.

I'm not saying no site can look good in portrait or zooming cannot be reasonably painless, but landscape browsing does have a case on high-res MIDs.