I've tethered for over a year now. I loved foxfi, but it doesn't work with Jellybean (doesn't matter anyways since JB already has tethering built in). Last time I checked, foxfi has an add-on which uses a web proxy server to hide tether usage.
I pay for 20G a month and prob spend half of those on tethering. I've been doing this for awhile now with no repercussions yet, so I honestly wouldn't worry about getting in trouble. However, that's just me. As a precaution (which could be real unnecessary) I've disabled all verizon apps on my phone just in case.