Many threads on this issue. Whenever one disappears another rises like a Phoenix. Simple answer is that there's no documented case on this board of anyone being charged for occasional tethering of a Droid.
On other questions, the previous poster is correct; there is no 5 gig limit for the Droid. Just a prohibition against tethering, period.
The Incredible does support tethering as a Verizon supported feature. However, that plan does have a 5 gigabyte monthly limit and it involves an additional $25 per month charge. That is actually a "sale price" compared to the usual $30 charge. To further confuse matters, there is also a $10-$15 a month tethering charge for unnamed "android" devices. It, too, has a five gigabyte limit.
As to whether Verizon can theoretically determine if you're tethering, the jury's out. Suffice to say that it doesn't appear they're interested in sleuthing out those who are doing so on an occasional basis.
Suffice to say, also, that Verizon has managed to confuse this entire topic so badly that I doubt anyone at Verizon has "the last word."