Here's a picture of my iPad displaying an uncropped, unzoomed, page of a US-letter format PDF. As you can see, the aspect ratio of the iPad is pretty much a perfect match for such documents.
EDIT: It's not a very good photograph, I'm afraid. Poor lighting (the iPad bezel is actually white
). It's a lot clearer in reality than it looks in the photo, but hopefully the photo at least shows that it is easily readable.