I contacted a rep on Twitter (just to test the knowledge waters again) about how to keep track of the tethering usage. I was told to look at my line usage total. Either Verizon didn't think this new plan out all the way, or they aren't (at least at this point) going to make it available, to where the user can keep a running total between the tethering and the phone data. If a user does use more than 10GB of tethering and is throttled to 3G and the data is all lumped together with the monthly phone total, that means that users could see their phone data speed throttled as well, unless Verizon has the tethering and phone data separated in real time behind the green curtain.
It strikes me as odd, that Verizon is advertising this new plan the way they are, without the user being able to see data usage from both avenues of usage, given that they clearly state throttling after 10GB of tethering.