Today I got my membrane-Potentiometers (100mm-Hotpot) from Watterott. I had to wire a 10k resitor to between the "wiper" and ground. If this is not done, when the membrane is not touched it, and therefore the AD-converter-input, doesn't have any scecified contact with ground or 3.3V so it will send random signals, which cannot be filtered. With the 10k resitor, the value will be zero when the membrane is not touched, but this can easily be filtered by software.
Like this the pot works quite well, no jittering. I have a round one and 8 linear potentiometers.
I also got pressure sensitive resitors (sadly I did not manage an own post for it, I was rahter busy).
Very simple wireing, just the pressure sensitive resitor between 3.3V and the AD-input and a 10k resitor between the input and ground. This works quite good and is fun to press =).
I also got my 100 mini-arcade-buttons, yeah!