I like to read - I've always enjoyed a good book series. And late nights that I was up with a newborn I got a lot of reading done, but it is hard to do without a good light...and no, I don't have a Kindle like all the cool kids, but I did use the Kindle app for my iPhone. It worked out great b/c I never had to turn on any lights. It has a lot of great features, too - easy to search and highlight.
So, last week I upgrade my iPhone to the iOS4 and when I did I downloaded the iBooks app - so far I like it as much as the Kindle app. My one complaint so far, though is that I haven't figured out or if I can lock the screen aspect. I read laying down a lot and that means holding my phone sideways, but not necessarily wanting it to go to landscape view. On the Kindle app I was able to lock the aspect so that even if the phone was horizontal, the aspect would stay in portrait. So far, that is my one and only complaint regarding iBooks. I just bought my first book through iBooks though and I haven't read very far so I don't know what other pros & cons I'll find.
I do like the library on iBooks much more than the one on the Kindle app, too - it's a nice layout as opposed to just a list of the books. It's only aesthetics, I know, but I still like it! It's just a nicer way to browse your books!