Needless to say, the tools to go peeking around in other people's libraries are much fun ... it's just that all these "one user" books are starting to make me feel a bit like a FREAK!
{edit}
O.K., so I went back and checked on the "manually entered" things and they're showing up with multiple users (or not), so I guess they combine all editions of a particular work for the purpose of figuring out who has it in their collection.