I've been working on it for a few months now... The product had several iterations, first as a cappuccino app, then as a Mac app, then finally I decided I'd learn more by building an iPad app.
I didn't build a universal app because I didn't have the time to make it. I wanted the experience to be great, and I wanted to ship by December (I was three months late). So I can't comment on how difficult it would be.
I am a core team member for the Cappuccino Framework, so I know Cocoa (on OS X) pretty well... The transition for me wasn't too difficult... I just used the apple documentation.
How much time did it take you to develop?
Why you did not do combined iPhone/iPad app?
Based on your experience, is it more effective to develop combined app or separate iPad and iPhone?
What learning resources would you recommend to start developing iPad apps for a newbie?
thank you