The iPod nano could be Apple’s answer to “How would a product evolve over time if its designers had a multiple personality disorder?”

Yesterday, at their media event, Apple introduced the latest in the line of iPod nanos. I’m sure the new nano is a fine device, a worthy successor to the previous generation. But come on!

One year the nano is long and skinny. The next year it looks almost like an iPod shuffle. A couple of years later it’s back to long and skinny. As if that is not enough, in between these flip-flops there was briefly a third basic shape: squat and fat.

Then there’s video support. Now you see it, now you don’t. One year, the nano doesn’t play video, the next year it does. Then video is removed. And now it’s back again.

Apple has never offered a clear rationale behind these shifts. They occur for no apparent purpose other than change for change’s sake.

Yet somehow, with each iteration, Apple wants to convince us that the latest offering is the “best design ever.” This is getting to be a really hard sell. Following the shifts in the nano feels more like watching a pendulum swing than forward progress.

I half expect that Apple will someday introduce a new nano as “the second, perhaps the third, most amazing nano we have ever made. The best one was three years ago.”