Personally I don't mind two screens, especially if they can display independent data. For example your ebook on one and mp3 player on the other, or a stock ticker or something if it has wireless (ok not a continuous ticker but you get the idea, maybe RSS).
The other question that comes to mind is power consumption. Is it more energy efficient to update two screens at once or less? Overall though I like the clamshell like design. I guess we will have to wait and see where iriver takes this if anywhere.