I don't have a DX, just an iPad, Xoom and 1st gen Kindle. But from those experiences, it's not the form factor that bothers me - it's the natural continuous access of the ebook format. I can't read PDFs onscreen for much the same reasons.

When I read technical books, I scribble; I dog-ear; I add in postits everywhere; on textbooks, I even highlight and deface quite happily. And this helps me fix in my mind where reference information is: it's the green post-it in the corner. It's the page with the drawing of a dog in the top left. (I seem to have a very visual memory for recall.)

I just cannot, no matter how hard I try, reproduce that experience on an e-reader. Yes, the features are mostly there, and search is a very nice bonus - it also works quite nicely for continuous following of tutorials - but the general way I consume these books just doesn't translate.

The slow pages turns are a killer. Especially with PDFs. "As shown in Figure N" for any value of N not on the current page was what basically killed the usefulness of the device for me.