I love all things adjustable, flexible, and customizable. People's needs change over time, and it's nice to have furnishings that are able to adapt to those changes. This bookshelf makes me drool. The verticals are completely notched out at regular intervals, making it easy to move the shelves around and turning that functional aspect into a design element. Such an improvement over those ugly vertical lines of peg holes running up the insides of a bookcase.
Oh, and the rest of the project is lovely too. It is a Manhattan apartment designed by Len Morgan, featured in Elle Decor November 2012, in the article Made to Measure. Photos by Mikkel Vang. A couple of my favorite shots of the project are below, and more are available on the Elle Decor site.