Grandfathered unlimited data plans on Verizon = no free tethering.
Data limit = tether all you want, because we'll be happy to A) bill you for any overage, or B) upgrade your data plan "to better suit your usage."
If you do have grandfathered $29.99 unlimited data AND a 4G smartphone, you can officially add unlimited wifi hotspot for another $30 a month.
Personally, I have unlimited + wifi hotspot. I could probably circumvent the $30 fee, but I won't. For me, it's not a bad deal for $59.99 a month. I've been hitting 20 GB in recent months, which would be a lot more expensive on a measured plan, even if I had a double data promo. Verizon gets lots of money--maybe not as much as they want, but certainly more than enough--and I get lots of mobile data for my road warrior ways. It's win-win as far as I see it.
If Verizon ever starts sending me nastygrams about "excessive usage," aka, wanting more money, I'll be more than happy to send my money elsewhere. With AT&T finally starting to get their asses in gear network-wise, and Sprint and T-Mobile getting new cash to do the same, I have options.