My goodness. I've never managed to "actively use" the tablet for anything approaching 8 hours solid, although I've come close, while using it with Maemo Mapper to track my route through the backcountry. The battery was fine. But the screen was off for most of that time.

I also used the tablet for many hours in a row (4 or 5?) while on a plane to Europe. I needed to use an external 4AA battery pack to supplement the tablet's battery in that case, since I had the screen on the whole time...