Just based on the blurbs, it looks very good -- a simulator plus debugging on the native device is the best of both worlds, and a 70% royalty deal for apps over iTunes is quite good.
The iTunes distribution channel is really a more important aspect than a lot of people understand. The ability to distribute larger applications than the over-the-air limits and effectively market your title with more than a dozen character deck name, combined with the reasonable income split make this look like a very interesting market. This type of developer / customer interaction is probably the wave of the future for mobile devices, it will be interesting to see how quickly the other players can react. Based on our experiences with the carriers, I am betting not very quickly.
Carmack is a well known programmer who cofounded id Software and was the lead programmer of the popular Doom and Quake software titles.