I never even gave this a second thought, its only partially related to the 8051.

I wrote a program using a table for data instead of the serial port. The PWM loop would execute, then lookup the next position from the table. I played around with making some patterns and then I attempted to make solid shapes to tune the laser projector box itself. I realized that shapes which should be easy (square, triangle) were not smoothed around the corners very much. I looked for hours and didn't find any reason this should be. I was using adequate time delays after each location - the laser's seeking to each position should have no problems like this. I was stumped. An hour ago I found the solution. I was in the kitchen getting some food and it just hit me that the laser module was driven off of the 8051 SBC board I built. The input voltage fed through a 5V regulator to a 50uF cap - this was all that was smoothing the 5V side; after all - this board was not designed for this, especially to drive 2 motors and a laser module. Sure enough, looking on my oscope revealed a nasty 5V line on the power side of things. I added a 1000uF cap, and the line instantly became smooth, and the shapes instantly became perfect.

Reloading my serial program from the earlier post, it worked much better. Still not perfect, but this time I'd say only 1 or 2 out of 20 positions are being drawn wrong.