I tried this yesterday but the results were not too promising.My dev environment is a Macbook not connected to ground. The sensor is a 3"x3" piece of aluminum foil that I stuck under the cardboard of a hardcover book, R=10MOhm. The sensing range for my hand was around 0.5" and for a single finger
I could just make out a tiny increase of values upon touching the insulator. Touching the foil itself yielded a nice huge delta. Replacing the 10meg with 20meg resistors hardly changed the results. Moving my hand closer to the laptop however, DID create a large change in values.
The docs say to use a grounded connector which means that you could only build tethered projects. Kind of limiting for an embedded device such as the arduino- it would be nice if both battery operation AND power supplies would yield similar results.
I have begun testing out the CapSense library this afternoon, and noticed that if I left the sensor on for a few minutes there would be a slow build up (higher numbers coming out of the capsense function) over time.