My 2 cents (programming books is basically what I read... mostly)
6" screens are too small for programming books (PDFs or regular ebook format).
If you don't even have landscape mode, is even worse. I tried that, trust me, and it is really frustrating. I've posted screen-shots here of how bad it looks. A 10" screen, let's say a Motorola Xoom, iPad, Galaxy, are much better on that.
If budget is a concern or you want an eink device, try to buy one with landscape mode. It won't cut off (or there is less chance of that) let's say, a Sony or a Kindle 3.