Do we Thunderbolt owners have to cancel this feature so we don't incur a continuing charge?
Right now on your account, the feature is listed as a free hotspot. Until the promotion ends, continue to use the hotspot at no cost. How it will work after the promotion ends: It will route you to a page after you enable the mobile hotspot and connect your pc in Internet Explorer to sign up for the feature and accept any monthly charges associated with using that feature. We will definitely not surprise you.
I hope this answers your question.
It's "supposed" to be an opt-in type thing so after May 15th, it'll prompt you to add the optional mobile hotspot if you try to use it. There are rumors that Verizon may extend the promotion due to the recent nationwide outage and flaky service since then.