I was actually introduced to GTD through seeing the e-book title on Sony Connect (their iTunes wannabe site). It was a couple bucks less expensive than the paperback, and the capacity of the Reader is such that you can have a few dozen books handy without even using a memory card, so as a reference it can be very good.
**Somewhat ironically, the graphics in David's book are very poorly reproduced on the reader, because the small page just doesn't accommodate diagrams very well when they're printed in landscape.
The Reader does make for great reading of novels and mysteries and such, once you get past Sony's wonky Connect software. There's even a DVD of thousands of publicdomain books available for $25, from Black Mask Online. Just don't expect to be able to read garden-variety ebooks you might have purchased elsewhere. Sony's Reader can handle only limited formats, which include Sony's proprietary,un-protcted PDF files, RTF and such.
I also bought a Reader for my daughter, who's headed off to Japan, where the device is curiously not available for purchase, and she loves it for her train commute and reading at home.