I eventually just started leaving my Cybook on all the time b/c it was losing the page so often. I'm not using an SD card, and I haven't done anything else that's been mentioned to cause problems.
Backing out to the menu before turning my Cybook off does seem to reduce how often it happens, but it still seems to happen. If I leave one book, read another, and go back to the first one, the page is almost always lost. For a long time I actually thought the Cybook was only designed to remember the page of one book at a time.
It doesn't actually bother me a ton b/c I just leave my Cybook on now, but has anyone noticed a change with the new software?