I have 4 quite large pieces and one of them on my ribs, I would say if the one on your shoulder hurt that the one on the ribs would be even worse.

I agree with all the others in terms of outlining tends to be a bit more painful, however if they are shading in many different colours on the one area then this is also painful. The more time they are in one spot like Rainbowbrite said anything is going to hurt.

They use the same needles for heavy colouring as they do shading (the ones that look like 20 tiny needles all in one) so colouring/ shading pain should be about the same.

Also depends on the artist and how they work...