My new Premiere XL will lock up frequently, usually when using menus in Tivo Central. It's happened while trying to access recordings, or switching menus. And once I got a black screen, with the time bar moving, but no recording showing.
I've rebooted it each time (I recently became aware of the thumbs down/up play/play suggestion but haven't been able to try it yet). After reboot it appears to work OK, although I have to re-record whatever I was recording at the time of the reboot.