The first dining room I ever saw that was also a "library" was a beautiful dining room set, paired with some "library" wall paper. Somehow, it didn't look as bad as you might imagine, but - not nearly as beautiful as these multi-purpose library/dining spaces.
For most people, formal dining spaces are one of the least occupied rooms in their homes, and should they have them- libraries [in any capacity] are as well.
By combining them, it not only gives a place to spread out your work and books comfortably...
But provides space for a pretty and unique alternative to wallpaper, mirrors, and art. I think it makes it ultimately cozy.
These dark dining rooms set the perfect tone for a romantic dinner for two any night of the week, or a warm and inviting friday night with friends in the dead of winter!
I have always loved the idea of displaying your favorite books on a big round table - they would be easy to remove to set the table, and provide for a more stylized look when your not using the table.