The GP2D12 as a system is showing 0.025" amplitude noise. The system includes low-ESR capacitors (1000uF) on VIN of the voltage regulator, another on VOUT, more for each IR sensor, and an 8th order digital filter on the raw sensor signal. The sensor by itself, with no capacitors, no digital filters, exhibits noise in the order of 0.3" amplitude. This is damaging to my motors and motor controller (heat!). The low-ESR capacitors make a huge difference, but not adequate by themselves. By the way, the previous plots show the effect without the digital filter (see magenta curves), but with the capacitors.
My ZX-40A microcontroller loops at roughly 150Hz, so as long as my program is faster than 25Hz (IR sensor sample rate), the 8th order filter does not interfere with the control system. I can increase the filter order, however I'm saving the throughput for extra code for the GBOT90. This project involves rotating the GBOT 90 degrees to have it balance on its two front wheels. So mitigating sensor noise is central. GP2D12 sensor variability has not been documented, so I thought I'd query the field. Thanks for your comments.