90 I hate to say it... but the real answer I believe is 90. I read that iPhone home icons are 57x57 with a 10-pixel radius. If correct, that comes to 90 pixels (well, 89.8) when working at 512. So I tested that out, and I believe it to be correct: * I filled a 20-pixel circle (radius 10) and line it up alongside the corners of icons from an iPhone screen grab. Perfect match. * I grabbed a super-size icon from an iPhone screen in Apple's PR area and scaled it up to fit my Photoshop icon template. I tried overlaying your 100-pixel corners on it, and they looked too round. 90 pixels looked good. (Or rather, 180 in my case, since I build at 1024x1024.) BTW, I've only built iPhone favicons (apple-touch-icons) which always have Apple's bevel and shine. If I were making a real app icon, I assume you have the choice to omit the bevel/shine and use your image as-is (minus corners)? Also, FWIW, to make a 1-pixel line at 57x57 (home screen size), use 9 pixels (on a 512x512 document). To make a 2-pixel line, use 18 pixels. In other words, whatever you want at home-screen-size, multiply by 9 when working at 512x512. (These values are slightly rounded and will work best at the very edge of the icon.)
