When you have iPhone apps installed on the iPad, chances are they are doubly-ugly: they look pixelated when doubled and their icons are even more ugly extrapolated from 57x57px to 72x72px.
Recently, David Frampton posted great idea how Apple should have done this (the idea got picked by Daring Fireball, TUAW and many others). While idea is great, it’s more than doubtful that Apple would do this.
What Apple would likely prefer is that you, as developer, make an iPad version of your iPhone app and use the full capability of the device. In the process, you’ll create proper iPad icons and no ugliness then. In the Apple’s DevForums, there’s a thread with guidelines on how to populate App-info.plist file and what icon files are needed.
In there, it says that for iPhone-only apps you need to populate
CFBundleIconFile key with 57px icon. However, if you move down a bit, you’ll find section on setting up universal app. Do that, even if your app is not universal and voila - iPad will use the proper icon for your iPhone-only app.
The settings above are from my Quickie to do app - here’s before and after:
Much better looking.