I can use any e-ink device as a monitor ... as long as it has a browser in it. Basically, I run a little web server on my PC that host a page that keep refreshing itself with littles images that form the print of my desktop. I coded this in less than 2 hours, very simple. It's working quite good on my onyx m96 right now as I'm typing this text.
So regarding the sony digital reader, I can already tell you that it is slower than the onyx, and slower than the sony prst2. Not only the browser, but the whole display is slow I believe. Not only that, but also the browser keeps freezing, so the refreshing is not working. That's just 1500$ wasted, just like that!
still, I intend to use it as a pdf reader.. How ironic.