i've got that installed too -- works great, but I certainly wouldn't recommend doing it all the time.
Verizon charges people for an extra data plan if they plan on tethering it, so it would stand to reason you may be "punished" if they catch you doing it without jumping through their hoops.
i agree with the previous poster, if you usually average 1.5gb per month, and suddenly you're using 3-5gb+, they are going to figure it out pretty quick.