I really liked this simple statement on mindfulness from Awakening the Buddha Within: Eight Steps to Enlightenment: Tibetan Wisdom for the Western World by Lama Surya Das.
The Mirror of Mindfulness
Mindfulness is the root of the Dharma.
Mindfulness is the body of practice.
Mindfulness is the fortress of the mind.
Lack of mindfulness will allow the negative forces to overcome you.
Lack of mindfulness is the creator of evil deeds.
Without mindfulness and presene of mind,
Nothing can be accomplished.
Lack of mindfulness piles up shit.
Without mindfulness you sleep in an ocean of piss.
Without mindfulness you are like a heartless zombie, a walking corpse.