It seems like this might be moot soon since unlimited data seems to be going the way of the dodo anyway. Assuming the T-Mobile merger goes through, Sprint will be the last carrier to offer it.

AT&T had also started cracking down on people tethering without paying, with the punishment being losing your grandfathered unlimited data. I imagine this wouldn't be hard for Verizon to do either, now that they've got data caps too.