I can chime in on the 'not remembering' side of the issue
It happens quite frequently. It is more likely to happen later in the book. It also is about guaranteed to happen in those cases where bookmarking no longer works.
At Bookeen's suggestion, I reformatted my memory card to FAT32 and upgraded my software. Still no joy.
This compounds my frustration with the ability to search through the book. I often re-read books and I want to skip boring parts. Paging through the book creates two problems 1) It's slow; and 2) Each page turn burns the battery. I can find that I've 'read' an old book in a couple of hours, but that I've spent as much battery as if I read the entire thing.
There really needs to be some type of search feature. You tell it a page range and it goes to the middle of the range. Then you tell it to go forward or backward and it goes to the middle of the remaining range, etcetera.
Finally, another related problem to the original problem is that it frequently 'loses' my sd card. It's 'easy' to fix. You click the card to remove it, then you reinsert the card. Even if the system is still on it will scan the card and load the books. However, since I have over 400 books it take quite some time to scan in the list.
Finally, that leads me to another suggestion I've left with the folks at Cybook. Everytime the unit is turned on it first loads in the operating system and then it loads the entire library list -- which takes a while (thirty seconds? a minute?). If I'm in the middle of a book, I'm not sure why it needs to take time to load the library. Why doesn't it just open the current book?