When setting up the wallpapers, you can pinch/zoom and pan them around to get them centered just how you like...the trick is, if you then rotate the system, you can do it again for the other orientation, and it remembers both. This way you could use a 1024x768 image, and then zoom in the portrait version so that it fills the 768x1024 screen without being ugly.
Awesome. Thank you for this one.