I started with the excellent Teehan+Lax PSD. My goal: to match the Apple iPhone 4 Simulator.
After resizing the button @2x I reduced the size of the drop shadow (pale highlight below button), inner shadow (top), outline stroke, and also added a separate inner shadow inside the bottom half of the button.
It's amazing to see that Apple went so far as to tweak these individual button styles for the Retina Display.
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