Wallpaper hint: 1024x1024
If you want to create or use an image as a background/wallpaper and you don't want it to re-size when you change the screen orientation, make the image size a square 1024x1024.
The iPad screen is 1024x768... or 768x1024 depending on how you have it turned. So if you create a portrait image to use as wallpaper and make it 1024x768, when you turn your screen to landscape, the iPad will resize the image because that "768" now needs to be upsized to 1024. That ends up with a blurry image. But if you make the image 1024x1024 to start with, the iPad just crops off the "extra" on the sides (or the top & bottom depending on the screen orientation) and doesn't do any dynamic resizing.
Again, probably a "no kidding" to many but it made me happy to have my picture of my kids crystal clear no matter how I turned my iPad.
MacBook Pro, Mac OS X (10.6.3), iPhone, iPad, iMac, MacBook Pro, MacBook, Airport Express and Extreme, ATV