It has been quite an exciting (and busy) night for Thrive owners and hackers. The community managed to root the device, enable Superuser Permissions, and flash ClockworkMod Recovery. Thus far only a handful of people have taken the plunge, so issues could still arise, but preliminary results are looking good. In their own words:
Mine is the second fully working Thrive with Superuser access, Dalepl was first, and austeregrim bricked his to get shell root so we could get the system dump. NatolX bricked his to prove they have an unlocked bootloader.
...Please note take this at your own risk, this is just a preliminary step, and I happen to know it might only work on the latest OTA for the Thrive (dunno about later Toshiba updates).