"The Buddha clearly stated the reason for practicing mindfulness: to uncover and eliminate the cause of suffering. That cause is desire. When its cause is absent, suffering cannot arise. At that point, the sutras tell us, one knows a happiness with no hint of anxiety to mar it. But that isn't because sights and sounds magically become permanent, lovely, and the property of Self. Rather, these impressions temporarily cease and consciousness touches a supramundane object called "nibbana," the unconditioned element. Although a mental object, nibbana, the "highest bliss," is not a formation at all; it is unformed and permanent. So the present moment is worthwhile because only in it can we experience nibbana - complete freedom from suffering.

Yet can't sense-impressions be pleasurable? Yes, but pleasure isn't the unending source of happiness we take it to be. In daily life we perceive beautiful sensations as solid and relatively lasting, when in fact they're only unstable vibrations that fall away the instant they form. Like cotton candy that dissolves before you can sink your teeth into it, pleasure doesn't endure long enough to sustain happiness. " 

What's so great about now? - Tricycle:  The Buddhist Review - Winter 2006