Graceful. Elegant. Beautiful. In modern Japan, butterfly tattoos are popular with woman. They're seen as feminine, and have longstanding associations with happiness.
In the past, however, macho warriors would wear butterfly designs into battle; they even became a popular samurai-clan crest. This could be because the insect's grace was a direct contrast to the blood on the battlefield, but also because the butterfly was associated with longevity and the souls of both the living and the dead.
Butterflies make an ideal one-point tattoo, or they can be incorporated into a larger design.