One of my complaints about the kindle app on the iPad was when you change to landscape, you only have one page, one really wide page. I found this makes it not as nice to read as the Apple iBook application.
Amazon have released an upgrade to the Kindle app on the iPad to allow 2 columns. This means that when you change a kindle book to landscape, you see two columns, so it looks like two pages next to each other.
This seems like a small change, but it makes the kindle books much more readable.