The New York Times has an article today comparing the Kindle and the iPad. The overall point of the article is that in the long run, a device that does many things will beat a device that does one thing (in this case, reading eBooks). Randall Stross, the author of the article, quotes Marianne Wolk, an analyst for the Susquehanna International Group, as saying that a surprising number of people who own Kindles and iPads are shifting more of their eBook purchases to Apple's iBookstore.
I don't disagree with the people who say that the Kindle is lighter and easier to carry, has much longer battery life and is easier to read in bright sunlight than the iPad. However, I believe that the key reason that the iPad is a better eBook reader than the Kindle isn't that it can do many things, but because it's open. In this case, open means that anyone can create eBook applications for the iPad or use the Safari browser to read eBooks, while with the Kindle, you're locked into Amazon. On my iPad, I have eBook reader applications from Apple, Amazon, Barnes & Noble and Borders. I can purchase eBooks from any of those companies and have them delivered directly to my iPad. I can also purchase and read eBooks from other vendors that use Adobe's DRM system, and I can read open PDFs and EPUBs from anyone.
The fundamental advantage of the iPad is choice. I don't expect Amazon to ever make the Kindle an open platform. I'm aware of the iPad's limitations when it comes to reading eBooks, and they don't bother me. By improving the Kindle reader, Amazon is fighting last year's battle. They'll keep selling the Kindle, but internally, I'm sure that they know that the dedicated, closed eBook reader has a limited life.