OK.
The SDK is an extension of the existing XCode, and it just gives you a new type when you say new project. it gives you 3 defaults, simple, UI frame and basic list.
From there, coding is similar to programming for OSX was until garbage collection came in 10.5 (ie, no garbage collection). You basically get some new view classes.
When you hit run, you get a large iPhone like window, with a few applications (such as address book, safari) and the application you have just deployed, and the application runs on the iPhone simulator. The applications (or at least the examples) don't run on a real iPod at the moment, as they require 2.0, which isn't out yet (they sort of hang in various places on a real iPod). However, when you do plug an iPod in, it appears in a new window and asks if you want to use it as a deployment platform.

All in all it is very simple to set up and runs very smoothly. If you have a mac and any programming experience, I don't see you would have any problem being able to produce applications for the iPhone/iPod quickly. I would imagine that now, one day after launch, there are hundreds of applications taking form everywhere, and when OS 2.0 and iTunes apps starts, there is going to be a massive choice.

If there was a way to program for maemo that easily there would be a lot more quality applications for the nokias now.