Well, that of course depends on who it's with, where it's placed, and how that place is used.
Visually, I think low hung art can almost always work as long as it's in a group. If it's part of a grouping that starts a bit higher, it can ground soaring ceilings, as in Casey's loft seen in pictures 2 and 3. The same holds true for spaces with white walls, such as in picture 4, where the art grouping spills over the bed and nightstands, reaching toward the floor. The effect takes the emphasis away from the expansive white walls, and places it on the bed arrangement just like a painted or papered accent wall. It can also even out a room that houses a bulky or attention grabbing piece, such as the black bookcase in picture 1, Casey's armoire in picture 2, or Melissa Warner's beautiful blue tufted sofa in picture 5.
Functionally, it may be a different story, and one that seems to be quite subjective. Beautiful as they are, the low hanging art in pictures 1-3 would probably be total goners in a house with curious young children, pets, or clumsy occupants— one tug or accidental brush up against the wall, and down they'd crash. However, above a high-backed, thick sofa as in picture 5, art need not abide by the general suggestion of 5-10 inches above....unless of course you're tall and prone to throwing your head back or if the artwork protrudes over the back of the sofa— unpleasant for sure. Bottom line: assess your living habits and those of the people who live with you before going for an ultra low look.
And now, what are your thoughts?