Welcome to the forum. Next time, please do a search before posting, as this question has been asked and answered a billion million times.
Long story short, Verizon CAN charge you and terminate your contract for using PDANet, as tethering without paying for Mobile Broadband Connect is a violation of your Terms of Service.
If you use it sparingly, you should be OK. You can keep yourself off their radar by only visiting sites you can also visit from your phone, meaning Flash games and Hulu should be avoided.
Right now, it doesnt look like Verizon is doing anything to tetherers, we havent been able to corroborate a single case of people being hit for unauthorized tethering. That being said, there's nothing to say that they wont in the future. This is not meant to be a scare tactic or "fear mongering" as some will try to say. Everyone who tethers should be well aware of the potential consequences, should Verizon chose to crack down on it.