Just read that John Carmack likes the iPhone as a dev platform. That reminds me of the fact how I started my iPhone engine Oolong Engine in September 2007. Initially I wanted to do some development for the Dreamcast. I got a Dreamcast devkit, a CD burner and all the manuals from friends to start with this. My idea behind all this was to do graphics demos on this platform because I was looking for a new challenge. When I had all the pieces together to start my Dreamcast graphics demo career, a friend told me the specs of the iPhone ... and it became obvious that this would be even a better target :-) ... at the time everyone assumed that Apple will never allow to program for this platform. This was exactly what I was looking for. What can be better than a restricted platform that can't be used by everyone that I can even take with me and show it to the geekiest of my friends :-)
With some intial help from a friend (thank you Andrew :-)) I wrote the initial version of the Oolong engine and had lots of fun figuring out what is possible on the platform and what not. Then at some point Steve Jobs surprised us with the announcement that there will be an SDK and judging from Apple's history I was believing that they probably won't allow to develop games for the platform.
So now that we have an official SDK I am surprised how my initial small scale geek project turned out :-) ... suddenly I am the maintainer of a small little engine that is used in several productions.