I second this. I use Paint.NET while developing image processing algorithms.
When I'm comparing results across multiple instances of the same image,
it helps to be able to select the exact same location across these images,
so I can crop to this and save. The nudge via the arrow keys definitely helps,
but manual numeric entry would be even more convenient.
Also, it would help if the range of the rectangular selection were displayed somewhere.
E.g. something like
top left = (10,90) | bottom right = (200,300) | width,height = (190,210)
Cheers!