Having logged a few hours now in games with controls near the bottom of the screen (dual thumbsticks), I can say that your hands tire out pretty quickly because

Having logged a few hours now in games with controls near the bottom of the screen (dual thumbsticks), I can say that your hands tire out pretty quickly because you have to hold the iPad so that gravity it prying out of your hands. Ideally, the right control would be in the lower right corner, and the left control would be in the upper left. This would give you a better, more comfortable hold on the device. Also, surprisingly, games can still be pretty immersive when your hands are obscuring a portion of the screen. Translucent controls do aid in that.