Rumors are abounding of Apple introducing hardware/OS that'll sense the motions of up to four fingers on a single touchscreen. Four times the fingers, four times the finger grease.
In other technology news, Mitsubishi Electric is showing a prototype touchscreen that senses the distance to your finger -- effectively adding the z coordinate.
By calculating the time variation of capacity in the z-axis direction, the acceleration of the finger approaching the panel can be detected.
Z detection is two-fold: speed and distance. The screen detects the speed of the finger's approach; distance is detected in 256-steps over a maximum distance of 20mm (just under one inch) -- about 325dpi.