[guguy]

Well, you know, on the reader as you say you can't power-off, you can
just enter in a kind of suspend mode in which the screen is turned off
and the cpu is in low-consumption mode.

And when it's in this mode, turing it on only takes a second and you come
back exactly where you stopped in your book.

Without this mode, for instance on the iLiad, when you want to stop reading
you have to turn it off. And later, to go back to your book you have to start it again
(which takes 1 minute) and open again your ebook. Of course you don't have
to turn it off but in this case the battery will go flat in max. 10-15h.
But on the sony reader you can stay in suspend mode for days and weeks...