Well, it most definitely was "internet" in the beginning, starting with the iMac. After that, peripherals and software were designed and named with an "i" to go along with the idea of ease of use, just like the iMac... but the "i" never really changed definition -- the definition was kind of dropped altogether.
I don't think it means anything now other than signifying that the application/device is consumer-oriented for ease of use. I never heard "interpersonal" or any other definition of the "i", but I suppose it's left up to the consumer now to define it -- or, maybe it's not supposed to be defined at all anymore.
...or maybe it still means "internet": internetPod, internetCal, internetChat, internetMovie, internetTunes, internetMac, internetSync, internetPhoto... NAAAH!