Ok, so for the record,

I have slightly more complicated sketch than the one below, but it has almost the same amount of jitter.
As far as processing sketches go, you cant get much simpler than this one.

And still, there is quite a serious jitter, or short jumps, between seemingly random frames.

Could It be my JRE? or my crapy laptop?

does it also do that on your machine?

anyone? Phi.Lo??

<start sketch>

float x, y;
float size = 40.0;

void setup()
{
  size(800,150);
  noStroke();
  frameRate(60);
}

void draw()
{
  background(102);
 
  x = x + 2.0;
 
  if (x > width + size) {
    x = -size;
  }
  translate(x, 75);
  fill(0);
  rect(-size/2, -size/2, size, size);
 
}

<end sketch>

The Prodigy - "One Love" jamming full blast in the backgound.