iPad + Kindle + Smartphone

Does anyone out there use both an iPad and Kindle in conjunction with their smartphone? It seems like there's quite a lot of redundancy across all three devices, and yet there's specific tasks that each device excels at in comparison with the others, such as watching videos or creating content on an iPad, reading on a Kindle, or doing mobiley things on a Smartphone.

Currently I don't have either an iPad or Kindle, "only" an iPhone, and was wondering what other people's experiences have been using one or both of those devices.