Just got my initial review of the iPad posted, along with an in-depth look at iBooks.
The main review is here: http://www.the-ebook-reader.com/apple-ipad.html
And here's the iBooks review with lots of screenshots and a video: http://www.the-ebook-reader.com/ibooks.html
I'm also going to post detailed reviews of the Kindle app and Kobo app in the next couple of days or so, depending on how side-tracked I get playing with the iPad, and then other ebook and PDF apps after that.
: Here's the link to the Kindle app review: http://www.the-ebook-reader.com/kindle-ipad.html
And the Kobo iPad app: http://www.the-ebook-reader.com/kobo-ipad.html
The Kindle app has a few different features than iBooks like being able to add notes, go back, change background color, and zoom in on images. But it's lacking a dictionary and search function. It says those features are coming soon on Amazon's website, and I bet Apple adds a note feature to iBooks sooner or later, seems odd not to when the Kindle app has it.
I didn't go into a ton of detail in the Kobo review yet because I have a feeling that they're going to release an update soon. But there are several screenshots and a lengthy video.