The image is at 2048×2048 resolution, so it will fit on a new iPad and scale nicely to most other devices. Don’t miss the new OS X Mountain Lion wallpapers too, they’re also all high-res and quite attractive.
Apple knows how to pick great background pictures, and the new default wallpaper from iOS 6 beta is no exception. You’ve probably seen the rippled water already in screenshots of iOS 6 from Apple.