You know that cool feature where the screen will flip and turn depending on how you hold the iPod? It makes it IMPOSSIBLE to use when laying on your side in bed.
Also, if you have callouses fingertips from playing guitar, the touch-screen is often unresponsive when you use your fret hand.
I never tried to use my iPhone whilst lying in bed, so I'll have to take your word for it. As for the "fret fingers", I have a Pogo stylus that I use when I need finer positioning. They are not cheap ($15) but work better than other "universal" stylii.