Hibernate is a Druidcrowd control spell learned at level 66. It is usable on beasts and dragonkin. As with most crowd control effects, any damage done to the target will end the spell. Unlike Polymorph, it does not heal the target.
In a PvE setting, Hibernate gives druids a tremendous advantage as it allows you to take on beasts much more powerful than yourself. A good druid can kill an elite beast mob of his or her own level and even one or two levels higher by alternating Hibernate and [Starfire].
Hibernate can be used to help crowd control in instances where beasts or dragonkin are present.
Like most crowd control, Hibernate doubles in function as a spammable counterspell: Even though the target will not remain asleep while players are beating on it, any of its abilities in progress (with a cast time) will be interrupted.
In PvP, it is good to use against a hunter's pet, a druid in shapeshift forms, and a shaman in Ghost Wolf form. However, due to its cast time, a good player can often shift out of form before the spell is done casting to prevent it from being used on them.