I agree... I love my 5" pocket pro! When I bought it I was looking for the reader with the smallest footprint, so it would fit easily into my purse. I mostly just read fiction books with no pictures, so a bigger screen really isn't necessary for me. I really love the compact size, and I can see just fine on the 5" screen without straining my eyes. It's much easier for me to read on my Pocket Pro than it is to read on my laptop. My laptop strains my eyes.
I think there will be a market for 6" devices for quite a while. Larger sizes (9 and up) are more of a specialty market, I would think. People who read a lot of pdfs, or books with a lot of large graphics. But for just the average reader, I would think the smaller reader would be plenty sufficient. I could be mistaken.