I've actually found a sweet spot for a tablet. More than a year ago I ditched my smartphone for a Nokia C3-00. This phone has 2 weeks (!) of battery life and I use it only as a phone - it never drops calls or dies. I use the tablet (Galaxy Tab 8.9) for everything my friends struggle on a phone - much bigger screen for reading, bigger keyboard, more battery. It fits perfectly in the bag I always carry with me.

Note that I don't compare it to a PC - a real computer is a lot more productive when it's around.