Optimistically, 100% of us are eventually replaceable by someone (or something) as capable (or more capable) and cheaper.
It leads to more unemployment, but the step from unemployment to poverty is wrong. As efficiency rises, poverty should diminish, or in other words, society's monetary support (basic income) for its people should rise in relation to GDP. It's hard to see a futuristic society (where most tasks are completed by machines) functioning otherwise.
I'd argue that we're (almost) already there. Right now in the UK it would be cheaper to scrap our entire welfare system and just give every man, woman and child in the country GBP 3000/year, no questions asked, no strings attached. A family of 4 could live on GBP 12k (tax-free) outside of London - and anything earned over and above that would be subject to taxation as normal.
It leads to more unemployment, but the step from unemployment to poverty is wrong. As efficiency rises, poverty should diminish, or in other words, society's monetary support (basic income) for its people should rise in relation to GDP. It's hard to see a futuristic society (where most tasks are completed by machines) functioning otherwise.
http://en.wikipedia.org/wiki/Guaranteed_minimum_income