For many users, the newest update to the HTC Thunderbolt has made problems with the phone even worse. The primary issue is that it constantly reboots throughout the day randomly. HTC is still working hard to rectify the issue, and some recent industry 'rumint' suggests that the issue could be fixed soon. Furthermore, Verizon wants to keep you a happy customer. So, if you are fed up and don't want to wait for the new update, reports are that you can simply take your phone in to the nearest Verizon store, and they will replace your Thunderbolt with a brand new one that doesn't have the troublesome update.
Source: ThunderboltForums.com via Droid-Life