A lot of professional designers get it wrong as well, and I can understand; it’s truly very hard to make an icon that looks as great as one from Apple’s bunch and blends in with the rest. I don’t mean to be an icon snob; I like diversity in my icons, and especially creative freedom. It’s more than just annoying, however, when creative and diverse motifs look extremely alien to their environment.
Part of the blame is placed on Apple who's iPhone HIG (human interface guidelines) provide a mere 378 words on icon design, with examples that are sub-par. But de With isn't just complaining -- he's doing something about it. Enter: Composition:
Sean Patrick O‘Brien and I are working on the very first Mac application that will be released under the Cocoia ‘brand’: Composition. Composition allows you to take any image and get a pixel-perfect preview of iPhone’s default effects at regular home screen size and Settings/Spotlight small icon size. It also lets you look at your icon in a virtual home screen to achieve a native look (and yes, both iPhone and iPod touch home screens will be represented), and export it for further usage on websites and other materials.
Best of all, it's going to be free.
Check out the pre-announcement for details.