Capacitive touchscreens tend to require electrical contact with the body to activate. This avoids accidental clicks due to non-body objects pressing the screen and provides slightly better accuracy than resistive touchscreen technology, but it also means that a nonconductive stylus will not work. a conductive one would need to distort the electric fieldof the touchscreen in much the same way as a finger, and this is tricky to do with a small point. This is one reason I prefer resistive touchscreens (built one into my Eee).