adamrice, I agree with your full story except for this part "Pretty much all the dynos out there generate the same 3 V AC power. The iPhone needs 5 V DC to charge, so obviously that won't work as-is, although there are a number of connectors."
Any standard dynamo delivers 6V AC and there is a version of the B+M Lumotec I think that delivers 12V AC. But the 6V AC will be sufficient to power a 5V source. I have been reading up on this quite a bit myself as I'm planning to charge my standard car GPS over a dyno hub so that I can use it on my bike when touring. I must say that I was completely clueless about electronics and that I still have pretty low electronics skills, but 'mI pretty convinced by the following little circuit to power any USB device right away:
http://www.arenddeboer.com/2008/12/2...d-usb-charger/
You can find more info on this here
http://yacf.co.uk/forum/index.php?topic=6672.60
and here
http://www.bikeforums.net/showthread...r-from-dynahub
The only potential extra issue that I see with charging an Iphone is that some models won't charge on a standard USB 5V. I don't have an Iphone myself, but I'm sure that there are some solutions available.
Any modern dynohub will do the job. Schmidt is the best and most expensive. The more recent Shimanos have caught up to a level that you cannot feel a difference anymore compared to the Schmidt hubs. I think the (huge) price difference is linked to the overall built quality and finish which is better for the Schmidts.
The biggest difference in pedal resistance will come from building an efficient circuit. The one mentioned above should be pretty good.
Another thing to keep in mind is that using intermediate batteries (4x 1.2V NiMH) will make the circuit potentially very easy, but your total efficiency will drop dramatically as charging batteries generally takes a factor 1.5 energy in/energy out. You loose out a first time when charging your intermediate batteries and the power that you have stored then is used in charging your Iphone (loosing out a 2nd time).
One warning : this types of projects can get very addictif as you can see in my other post here
http://www.bikeforums.net/showthread...rom-dynamo-hub
Have fun trying things, but be careful because frying an Iphone gets expensive (so test on an old phone or anything you are ready to see die).