Toshiba's just released an update that addresses the Thrive tablet's issues when coming out of its sleep mode. The update is available in the Thrive's "Service Station" app -- a handy little guy that manages your updates on the device.
Here's the official word from Toshiba:
A limited number of Thrive Tablet users have experienced a Resume issue when in Sleep mode. Toshiba has released a software update to resolve this issue, improving the sleep-and-resume performance, as well as enhancing the multimedia playback capabilities of the device. The software update can be downloaded through the Toshiba Service Station utility app found on the Thrive Tablet.
And that's that. If you've got a Thrive, get to updating.