The blue poison dart frogs are really poisonous.
Blue Poison Dart Frog (Dendrobates azureus), Toronto Zoo.
The poison of the poison dart frogs is used by the people native to their the range on darts and arrows to paralyze and kill prey even if the wound is superficial.
Poison dart frogs live in a jungle and their tadpoles have to live in small pools of water often inside bromeliads. Since they would have nothing to eat there the female frog lays infertile eggs to feed the hungry tadpoles.
It is generally not safe to handle a wild poison dart frog but in captivity they often stop producing poison. Some people do like to keep poison dart frogs as pets because of their bright coloration. Poison dart frogs are even bred in captivity for the pet trade.
Scientists currently do not consider the blue poison dart frog as a separate species but as a subspecies of the dyeing dart frog (Dendrobates tinctorius).
Dyeing dart frog (Dendrobates tinctorius), Budapest Zoo.
Further Readings:
Blue poison dart frog on Wikipedia.
Dyeing dart frog on Wikipedia.
Dyeing poison frog (Dendrobates tinctorius) on ARKIVE.
Pet Poison Dart Frog Information.