All members of the family, under whichever name, contain the anticholinergic alkaloids hyoscyamine, scopolamine and atropine. One annual species, Datura stramonium, or the thorn apple, so called for its spiked seed pods, was grown for its alkaloid content and used in medicine.
Datura was supposedly used in witchcraft to induce hallucinations. If taken one does not stop dreaming even when awake. Hallucinations caused by anticholergenics are extremely powerful from the point of view that they can create fully realistic 3d objects which blend in perfectly with the persons view of the world.
Datura stramonium is commonly called jimsonweed. It got this name from the town of Jamestown, Virginia. In the 1600s, starving settlers were willing to try anything. They figured that if they boiled greens, threw out the water, reboiled them, etc., a few times, any poisons would be eliminated. The toxins in jimsonweed are very strong; this treatment did indeed avoid death, but the settlers were dazed/stoned for several days.
The dose-response curve is very steep, so people who consume datura can easily get into the potentially dangerous zone.
Datura is also the name of a trance song by singer/songwriter Tori Amos. Appearing on her album To Venus and Back, the song features Amos reading a list of various plants that are growing in her garden over hypnotic piano and rhythms. She consistantly mentions Datura within the list, as if to indicate it is overgrowing and destroying her garden. The flower, in the song, is used as a metaphor for destructive relationships.