Basic Xcode app.

If you are familiar with Cocoa and Objective-C, you are pretty much there. You will just need to get yourself familiarized with the Cocoa Touch Framework. You will need the basic concepts of object oriented programming but the rest you will just pick-up as you go. Look at sample codes they have posted on their developer sites, they can be really helpful.

 

My suggestion would have been to follow the CS 193P courses from Stanford, but it looks like they very recently took those down.

Here's a link anyways, it looks like the new lessons should start getting posted on the fifth... they probably won't be to a particularly useful topic until the 12th or 14th though.

http://www.stanford.edu/class/cs193p/cgi-bin/index.php

Maybe if you dig around you can find the old stuff...

It looks like the iTunes store still has it.

Just search "CS193P" on iTunes U. It should return a Stanford course with about 23 videos and 17 lecture slide sets. I suggest downloading all of it ASAP, before that too gets taken down.

If you'd like the assignment packet PDFs, I have a few of the later ones still kicking around my computer.

 

I think that the learning curve is different depending on what your goal is. Are you trying to develop a simple application just to learn a new programming skill, or are you trying to learn so that you can develop applications professionally?