I have to say I was a skeptic regarding portrait mode, but I have to admit that I use it in the browser in portrait regularly, primarily for reading these forums, and with the iPhone version of Google Reader. I've got the half-press on the camera button mapped to the back function in the browser, and it rocks!

The only other app I run in portrait mode is the phone itself which is set for portrait only.

I find the rotation transitions to be glitchy and cause audio drop outs. If Nokia don't improve performance in that respect, they may as well forget further support for portrait mode, IMO. I'd be much happier with a slower rotation transition than the glitchy audio.

Generally, as far as my N900 is concerned, I'm a happy bunny