400 books is not a lot unless all on T2 memory. To have more responsive collections and Books in library tun off setting show covers for books and library. Covers will stil be shown on home screen.
Just another form of hording that gives people feeling of security and power. Gutenberg has over 40,000 books to put on your reader. Go for it. Hand someone your reader and tell them didn't know you could lift 9,000 books.