For me, there’s one thing missing when it comes to the conceptual design behind Apple’s iOS. That for devices which are clearly made for media consumption (although certainly not exclusively), there’s still no simple way of actually getting the media onto the device.
Say I have a tube map in PDF format for example. Shouldn’t I just be able to easily copy over this file from my computer? It bugs me that there’s still no easily accessible file system structure in the OS. I’m not saying I need root access, I just want to be able to save stuff. It’s equally (if not more) frustrating that you can’t save a file (for example a video) from Mobile Safari straight to the device.