I have just ordered a Cybook and am interested to see how I well it works, especially with PDFs and my eyes ! Also the reason why my post to this thread is so late (have only just read it).
As far as specs go, if as TS-Rick wrote the CPU is s3c2440 then according to :
http://www.samsung.com/global/busine...i=PartnoSearch
this family can be either 300, 400, or 533Mhz. And it isn't given that a faster CPU will automatically use more battery. Somebody would have to compare the CPU specs to find out whether that is the case or not, and if it is anything like x86 then just reading a document (without interaction) should't consume any more.
As far as "firmware" goes, the 820 may just be a newer Linux kernel to support the processor. And given the months between even the one of the most frequently updated Linux distributions, Ubuntu, every 6 months, it wouldn't surprise me that they don't release a new version that often (although it would be nice that a bug fix release appeared more often than that).
Given this is OSS the source code for 820 should be available somewhere which would make it easy to diff the differences between 820 and 796. I'll mail Bookeen as soon as my Cybook has arrived.
As for "This makes me doubt that there will be much support for at least the original system" (Manichean), given this is Linux based it should not be a problem (depending upon what other changes other than CPU they have made).