Brush strokes are applied to the canvas exactly one-half pixel down and one-half pixel to the right of where the brush cursor is. The same thing happens when stroking a path. This can make it difficult to do detail work.
I am zoomed to 1600% here. I had to draw the cursor because printscreen didn't capture it.
Image is not available
I have noticed several other small inaccuracies. Here I made a black pixel with a 1x1 path around it, then I rotated the image 45 degrees.
Image is not available
Image is not available
When viewing an image at less than 100%, there are some alignment issues between layers. I drew two red circles on the background with the pencil, then made a new layer with two white circles. I made a new layer and drew two white circles offset by a couple of pixels, then nudged the layer back over the original red circles. (the two white circle layers are now identical) When viewed at 50%, I get different results, though. Both screenshots have the red layer turned on. The first image has the only the first white layer on, the second has only the second white layer on.
Image is not available
Image is not available
If I crop the image, the second image looks like the first again.