As an owner of both an iPad, a Kindle, and recently purchased a Nook, I have to say that the iPad was not a Kindle/Nook/eReader killer at all. I will admit that I no longer carry around my Kindle, but I have the Kindle app on the iPad. To me, the iPad is just a super-sized version of my iPod. I do spend quite a bit of time reading on it, but would rather read
text on my Kindle. Easier on the eyes and lighter by half. Also the Kindle fits in my purse much better. But, I can't view movies, TV shows, play games, have access to the thousands of iPad/iPhone/iPod apps on any eReader. And the games that are now available on the Kindle and Nook are lame at best.
I bought the Kindle because it does a spectacular job at what it's meant for ... bringing portability and ease of use to my library. AND it allows me rudimentary web access in case I want to read a blog, look up info on Wikipedia, check a definition, etc. And I can make notes/bookmarks galore on my eBooks without guilt
If I were forced to give up either the iPad or one of my eBook devices there would be no contest for me. The iPad would go!