As an E-reader only the Kindle beats the iPad hands down, in my opinion. The Kindle is smaller, easier to handle for reading, draws less attention, and the screen is infinitely better in direct sunlight. The battery lasts for weeks instead of hours and the price is much lower.
I had an iPad for a few weeks and ended up giving it to a family member. Between a netbook, MacBook Pro, iPhone, and Kindle, I just didn't see much use in the iPad. It's great at consuming content, but if the primary goal is consuming books, then the Kindle is wayyy better.
That's my opinion anyway...