This showed up on my 23″ Apple Cinema Display today.
At first I thought it was a stuck-off pixel, but I made a image with a black and red pixel in it, and those are much smaller than this, and I can kinda see the red pixel through the spot.
So maybe it is some dust, or condensation between the LCD and the matte?
The pixels in the image are the blurry spots to the left and right of the anomaly.
