Not excessive
I have both and ipad and Kindle. I use the ipad for web, email, music/video and apps. I got a Kindle to read books for 2 reasons - the battery life and weight/portability.
The kindle is much lighter than the ipad. When I go out I don't always want to take my expensive and somewhat heavier ipad with me... but it's nice to be able to read while waiting, so the Kindle fits the bill. This weekend I will be sitting by the pool. I would never take a $600 ipad to the pool, plus there is the sun glare issue.
And the battery life on the ipad is ok, but not as good as the kindle. I found myself feeling "guilty" for reading for a few hours on the ipad...because of the added trouble of recharging. With the kindle I can read and read
Don't get me wrong, I LOVE my ipad. It's just not my primary ereader.