On the other side of this, people enjoy the temporary aspect of leaning the art. It can be seen as casual and you are able to move it about. Derek Larson says, "Leaning art feels effortless and casual. And it makes it easy to rotate pieces in your collection."
In Domino, the art is hanging and leaning. I do like the gallery style on the back wall though--look how low those pictures are!
Living etc. A framed poster (inexpensive art!) is propped on this mantle.