To rkomar: you are right, it's the torque (more than the weight) that makes holding a heavy ereader wearing. However, if you make use of a supporting point (a table, your legs, ...) the problem vanishes. After all, it's the same issue that comes up when you read a thick magazine (most of those weigh 1kg or more).
To DuckieTigger: I usually eliminate the margins (leaving only a few millimetres of "white" all around) from my pdfs before copying them to my ereader, but did not experience any additional difficulty in reading because of that. Maybe this changes from person to person?
Finally: what I would really like to appear on the (non-Russian) market is something like this:
http://www.plasticlogic.com/news/pr_..._sep122011.php
Maybe some of you have any news about its actual availability, in Russia at least?