With labour saving devices we use the time saved to do more work, not for leisure. It makes work cheaper, not obsolete, and we still need knowledge workers. After all, they're the ones designing the labour-saving devices and their tasks, aren't they? In days gone by, they worried about what people would do with themselves once machines had made manual labour practically obsolete. They simply failed to understand how much work we can find for ourselves as a species.
Mokalus of Borg
PS - They also failed to account for greed.
PPS - If you can get the job done twice as fast, you can make twice as much money.