10 shot multiple exposure of tall lob lolly pines in snow & fog. Posted a vertical version of this yesterday - http://www.pbase.com/ed_k/image/91826057
I try to make images in both orientations when possible. Having an L-Bracket on each body (I shoot 999 of 1000 on a tripod) makes this easy to do. I don't shoot for publication (although the National Park Service uses my "volunteer" work often) it's a good habit to get into. Also, if the publication is a magazine or book cover (and I do have a book cover to my credit) subject placement becomes important. If the subject overlaps where the publisher normally places text, that's not good.
Aesthetically I guess it depends on the maker/viewer. Myself, I usually prefer a vertical for things that grow - like tall trees - as that orientation follows the natural lines of the subject. I also like it for landscapes since I much prefer my landscapes to have a strong foreground element. Vertical allows the sweep from this foreground object through the mid-ground and off into the distance to come through whereas the foreground to distance space is often too constricted in a landscape oriented image. In fact, if the foreground subject is something like a single flower near your feet, vertical with a wide angle lens and the camera pointed somewhat downward is the only way to go.