Up to now, these devices have mostly been way too expensive - close to iPad prices - or cheapo devices (apad/hipad) with serious shortcomings, e.g. No Android market and ancient versions of the OS. In my case, I paid £160 for a device with poor quality control, had to return it as the wifi was broken. I changed my Google password a while ago, which broke Market and GMail and means I have to hard-reset in order to install any new apps. (There was no error message from those programs and had to trawl through forums to work out why there exiting immediately.) So tne 7" devices today have not exactly provided the out-of-the-box iPad experience.
"it's all about the software" as many hardware people say these days. If Amazon can build a smooth user interface, it will be the first inexpensive mini-tablet which "just works".
I get that 7" works for reading literature and has better portability. That is Amazon's home market.
The problem is that 7" makes full document reading (pdf, web pages, code, etc) hard.
I'd pay for an 12" iPad, since my eyes are older than 40. (-: Maybe I need a fresnel lens, Brazil style? :-)
The only thing I would like to see from Amazon is a larger display version that is suitable for technical books.