I'm not sure what the correct size should be.
Many sites seem to repeat that the apple-touch-icon should be 57x57 pixels but cite a broken link as their source.
Hanselman's and playgroundblues's comments suggest different sizes including 163x163 and 60x60.
Apple's own apple.com icon is 129x129!
See my related question: How do I give my web sites an icon for iPhone?
It seems that Apple guidelines as of August 3, 2010 now include the "High resolution" images (for iPhone 4) in their "required" icon sizes.
Looks like we need to provide both a 57x57 and a 114x114 image now, as well as a 640x960 title image.
See Custom Icon and Image Creation Guidelines (Javascript required) which is part of a whole document:
2.1m questions
2.1m answers
60 comments
57.0k users
