Thanks for the info guys.
Some more information.
I have linearized the output from the sensor(s).
However, the raw values also fluctuate over time.
The measuring distance (25 cm) should be in range of the sensors capabilities (30 cm).
And I have capacitors in place to stabilize the voltage.
(One big and one small, based on the information in the data sheet)
There are other sensors on the same 5 volt line (flex sensors).
So, if my voltage supply was not stable enough for the IR Rangers,
(or destabilized by these sensors) would that not cause readings for the flex sensors to also jitter?
I was thinking that it maybe had something to do with the frequency at which I read them.
The datasheet http://www.sparkfun.com/datasheets/Sensors/Infrared/GP2D120XJ00F_SS.pdf specifies
a "timing chart". I cannot make much sense out of it, but does this imply I cannot read the voltage all the time?
Does the voltage from the sensor need to stabilize before it's ready to be read again?