I love the old-fashioned (and practical) touch of a library ladder. While I often think of libraries as staid, traditional environments, this space proves that they can be modern and fresh, too.
Hosting the party in an unexpected setting can enliven the atmosphere and help guests mingle during those in-between moments of drinks/dinner/dessert. A room filled with books adds a sort of unspoken intellectual sophistication, which really helps during that inebriated game of charades later on.
Bookshelves don't have to be kept to a separate room. Discreetly incorporating them as one wall of a large space adds a great vibe and suggests a house of learning.
the idea that the "library" can be part of the main living space, which is esp. nice if the people that live there have a love of books, almost like a statement, without having to say anything