From Something Really New:
We can distinguish mere novelties from real innovations fairly easily. The really simple test is to show the change to someone and wait to see if he describes it as “cool.” That pretty much settles the matter. Cool is often clever, but it is rarely useful. We are attracted to cool and we will tell our friends about it, but not many of us will buy it.
Can’t fully endorse it yet, as I’m not very far, but seems like a pretty good book about product design: