The contrarian in me would like to support spelling Internet with a lowercase i, but I don't think Internet is a common noun: there's only one of them, after all.
Steven Jones, a communications professor at the University of Illinois at Chicago and president of the Association of Internet Researchers... [said] "I think the moment is right [to treat "Internet"] the way we refer to television, radio and the telephone."
There is more than one telephone, radio, and television. In your house, probably, even: the transceiver is called by the same name as the technology. The parallelism is lost on Internet: Internet transceivers are called computers, not internets. If the word is really short for internetwork, that makes sense: your computer by itself is not even a network, much less an internetwork. (Yeah, radio is kind of like that as your radio is not the thing doing the radiating; I'm not sure how that fits in a convincing scheme for either side.)
A historical problem (it seems to me--I didn't read this point somewhere or anything) is that if you get two five node networks to crosscommunicate, you don't have an internetwork, you have a ten node network. Internet is an emergent property of a bunch of island networks being able to crosscommunicate; Internet is the entire TCP/IP übernetwork. If you have a mini-Internet, you don't have "an internet," you have an intranet or a network. Internet is the emergent property of connected IP networks under distributed ownership.
You could also make the argument it should be lowercase in the same way sky is a common noun, yet there's only one sky above us. We speak of "blue skies" in a way we don't speak of "slow internets," though. We have "slow networks" instead. It's like Internet is the hyperplural of network in some way. It's generally a linguistic nightmare, and trying to change it from its natural state of rest won't help.
