Based on Maslow's work, Dr. Peter Hancock came up with a model of what it means for a product or service to be "usable", in his June 2005 paper, Hedonomics: The science of enjoyable human-technology interaction. Like Maslow, Hancock comes up with a hierarchical model. At the bottom is "safety/pain avoidance", the next layer "functionality", then "usability", followed by "pleasurable experience" and, at the top, "individuation/personal perfection".
What Hancock suggests is that in order to be considered usable, a thing (or service) must be both pain free and do what it's intended to do. For example, if a lamp gives me an electric shock every time I turn it on, Hancock would not consider it to be usable. Or if the lamp was beautiful and pain free, but didn't work, that would also not be usable.
But Hancock's model gives us something more -- it gives us two more layers beyond usability that were, until now, implicit. What that means for us as designers and developers is this: neither functionality nor usability should be where we stop designing or implementing. The overused example of the iPod is over-used for a reason: it's a fantastic example of Hancock's fourth layer, pleasurable experience.