Don't want to talk to myself, but:
I don't think the code in that link is correct. Good approach, but there are problems with the implementation - should not use the same pin to charge, discharge, and measure; also should not be using a digital pin to measure the decay rate (HIGH is 5V, but LOW could really be anything below 5V).
I have some code I'm testing now, using separate pins to charge and discharge and an analog pin to measure the time. I started with the code in the capacitance meter example:
This code works very well. I was able to accurately measure some caps I have from 100 uf down to 2 nf. It's spot on.
But I have run into a few issues using this with the sensor. The capacitance of the sensor is very low, regardless of humidity. But the biggest problem is I simply can't get the capacitor to charge to 5V no matter how long I keep the chargepin on. It will charge to around 1.61V and if I breathe heavily onto it I can get it to charge to 1.78V.