Another impression: I put onto the Story HD a 125MB PDF I got from Google Books. (I didn't download it directly to the device from there, I put the copy onto the device via USB.) It's a very cool file, the first Hebrew concordance of the Hebrew scriptures (1581). 835 pages or so. It is of course entirely scanned images. I opened it up, told it to go to page 800 or so (since the back is the front and the front is the back) and I paged around a bit. The Story HD was very responsive, moving through the file quickly and then showing images quickly. My comparison experience is a Kindle DX (not the latest version, the one before that), which is significantly slower.
The images were clear, despite the small screen, although since I don't read Hebrew at all I don't know if the little dots were rendered clear enough. Why do I have the book at all if I don't read Hebrew? 1581! Very cool looking!
Also, it was the biggest PDF I had around, for the test.