I remember being horrified by Stephen King's short story The Jaunt:
http://en.wikipedia.org/wiki/The_Jaunt
The story takes place early in the 24th century, when the technology for teleportation, referred to as "Jaunting", is commonplace, allowing for instantaneous transportation across enormous distances, even to other planets in the solar system.
any conscious being goes insane or dies after being Jaunted: while physically the process occurs nearly instantaneously (the condemned man traveled two miles between two portals in 0.000000000067 seconds), to a conscious mind it lasts an eternity and beyond; one is simply left alone with their thoughts in an endless field of white for an unthinkable length of time (suggested to be billions of years). If one is stuck in this horrific limbo, their mind will either shut itself down or be driven insane from the lack of external stimuli. However, the father is careful in his wording to keep from scaring his family.
http://en.wikipedia.org/wiki/The_Jaunt