My personal experience with Amazon over the past year has been very positive. I have a Kindle and IPONE reader. I use them both extensively.

The big difference with the Amazon ebook process is they maintain your copies for you, you can down load them to the device of your choice when ever you want by logging onto your account. Laptop, Desktop, IPHONE etc. The only DRM they apply is by the account. Once you purchase on your account, you can read it on any device as long as you log onto your Amazon account with that device.

Also they have a kind of loaner capability that I have not used. You go through a simple process to loan it to another account holder and they can open it. Only one account can open it at a time and after some interval it goes back to your account long term

One advantage is that Amazon maintains the data for you so you dont have to have your own library with all the implications for maintenance, backup etc.

My guess is the Kindle App, will work with the iPad. On the Kindle site is says coming soon to Mac and already I'm seeing some big changes happening to the Kindle site. They are showing some books as "formatted for a larger screen" however, that could be for their Kindle DX model (larger size kindle) Also they are offering more FREE books and reduced prices, in order to stay competitive.

I personally really like their services, I can sync my Kindle, PC netbook, iPod Touch, iPhone all with one Kindle account and read on whichever device I want and not lose my place. I'm hoping the iPad will be included as well. Actually, I would be really surprised if it isn't, since most of the apps are supposed to work on the iPad and Kindle is one of the apps.

2 days till Pre-Order!

According to this cnn comparison article, the itunes/ipad book format uses "open ePub format":

Apple iPad vs. Amazon Kindle chart | Crave - CNET

From what I'm reading, this is a standard ebook format and not a specific Apple format. I'm sure their DRM will be Apple specific, but the book format itself appears to be a standard ebook file type.
So, this is good news. We should be able to download ePub format books from sites like ebooks.com and they should work in the ipad book reader app. Keeping my fingers crossed.

Here's another article indicating that Apple is using the standard ebook format:

The iPad iBooks App uses free, open-source ePub format | Cult of Mac

Sounds like we can buy books in ePub format and read them just fine in the Apple ebook reader. This is awesome news. I'm bookmarking a bunch of pages on ebooks.com now.

So say I have 10 free books in ePub format how do I get them onto the iPad??

I'm only speculating here, but I imagine you'd do it the same way you would with music and movies. Just drag the files to your itunes window to add them to your itunes library. Then the next time you sync, the books will be available. Of course, this depends on whether or not they are integrating the iBook reader with the iPod app that syncs with itunes.