I ordered a couple of small lenses from Surplus Shed (#L4471) to try out as macro lenses for the iPod Touch. They arrived today, so I tried taking a couple of test pictures with them taped to the front of the iPod. I was a little disappointed, as I was hoping to get tighter close-up with it. So, naturally, I stacked the two of them together to try it that way. This is the result.
These are images of the pixels on my monitor (~92 px/in ) taken with the iPod and my DiMage Z2 in SuperMacro mode. The image resolution ends up being very similar (in this test each screen pixel ends up being about 12 pixels across), but the Z2 does a better job overall, with better color and, of course, more pixels overall. The iPod does pretty good though, certainly acceptable for quick shots of stuff. I'd like to try another lens with a different focal length (these are 51mm) to see if I can get up closer.
Here I got a picture of a US penny. The Z2 will take better macro pictures than this, but I didn't put any effort into setting up, I just snapped a handheld auto-focus picture with ambient light. But I did the same thing with the iPod, so it's a reasonably fair comparison of taking a photo under these conditions.