I used to use the Kindle app on my iPhone. Well, I still do, but I also use it on my iPad 2.

Thoughts:

1) The Kindle app is better than iBooks in my opinion, as it has white-on-black (or sepia) built in, the dictionary stuff, and notes/highlighting. An interesting twist with highlighting: if enough people highlight a particular passage, you can tell the Kindle app to subtly underline it for you as well.

2) Reading non-Kindle books (PDF, ePub, etc) is not possible without an actual physical Kindle reader. I use iBooks for that.

3) Much as I love reading a real, tactile book, the Kindle on the iPad is not a bad substitute. It's about the size of an open paperback, and the auto-bookmark features are well worth the change in format. I find that I have the time to read the books on my phone or iPad much more often than the real ones at the house, because I can read in line at the post office, prop it up while I'm eating at my desk, etc.

4) Reading at night without a nightlight is more useful than being able to read in bright sunlight, in my opinion.

5) Auto-bookmark rocks my face. Read a bit in line on my phone, go back to the office, pick up the iPad and it asks if I want to advance to the last read position on the phone. Nice.

6) Because of the time-to-read factor, I find myself buying many more eBooks than physical. I have two real books at home that I started months ago, and in the interim I've read probably 10-20 eBooks.

7) A phone is a much more portable form factor than a paperback, and the small screen really isn't a detriment. Plus I always have my phone with me. I don't always have a Doc E. E. Smith novel, however.

8) With the apps for phone and tablets, I don't see why anyone would need a physical Kindle or Nook. Unless they like to read on the beach in bright sunlight or something.

9) Due to price and availability, I have yet to buy a book through iBooks. They're all Kindle, except for one ePub technical book I bought through Packt.

10) You can find eBooks for titles that you'd never find in a bookstore. It's like the difference between Netflix and a movie store.

11) eBooks are more expensive than paperbacks, less than hardcover. Although older titles that are out of print or not in demand are usually quite cheap.

12) Sample books on Kindle! Read the first couple of chapters and find out that you can't stand the book before you pay for it. Actually, get the free app for your phone, tablet, or computer and try a book out before you buy the physical version too.

13) Books over Wifi is much better than discovering you really only had 3 pages of prose and 40 pages of glossary left in the paperback you brought for a 30-60 minute wait.