When I used to leave them on my reader, I'd leave it at the end page as the most full proof method to know that I've already read the book. Never have to bother moving it into the "books I've read" collection, etc.
But now I just delete it from my reader. I only keep about 100-150 books on my reader at once. When I had over 1200 on my reader, it slows the reader down.