The title says it all, I would like to create a potentiometer (digital based) with the use of capacitive touch. For example, a metal sheet could be used as the slider, and you put a finger to change the output (using arduino).

 

If you have room for the PCB, this might be an option. Also the hookup guide linked from this product page has a lot of capacitive touch info on it that might help:

http://www.kr4.us/sparkfun-touch-potentiometer.html

Not capacitive, but this is another touch based pot:

http://www.kr4.us/spectrasymbol_bymfg_16-0-1.html