Interesting idea! I just bring my Apple Bluetooth keyboard if I suspect I'll be doing any amount of typing. I don't have much experience with Android tablets, but the iPad on-screen keyboard is pretty much the same size as their regular keyboard.
The whole thing about not having physical indents doesn't bother me much because you're looking almost right at it the entire time, whereas on a computer with a physical keyboard and monitor, you're looking straight ahead while the keyboard is lower. Keystroke lag causes most of my errors on my first gen iPad.
