I see them in Stacker machines pretty frequently, but since the difficulty on those is pretty high (for the top prizes), you can be pretty sure that you won't have to pay out too many ipods.
With a skill crane, the difficulty is much more difficult to measure. It's really dependent on a whole lot of factors (how is the desired thing laying, what's on top of it, etc, etc). I'm not sure you wouldn't end up paying out a lot of ipods.