It depends on how quickly it happens and due to what pressures.

In the last 50 years manufacturing jobs have plummeted while productivity has risen. This has been largely due to technological innovation both in terms of process engineering and the automation of labor. Quality has improved, costs have dropped, angels sing the praises of automation.

But what has also happened is that many of the labor intensive jobs simply moved somewhere else instead of automating. That's going to be due to a whole lot of factors but there is a large investment of capital in automating an operation and if you're only going to automate to produce one version of something (an iPhone for example) you might continue to have a more flexible operation staffed with trainable jobs (FoxConn) and efficiency improving machinery where possible.

But what we've seen here in the mean time is cheaper goods, built for a population with stagnant income. That's about exactly what you would expect as an economy pivots from one segment to the next. Especially when you consider that the amount of people not even seeking employment is huge. The question becomes: Are we already seeing the short term effects of a fast changeover to replacing low skill workers with robots?

We also need to consider what a 'robot' is. It's almost never going to be humanoid because for most applications the human form is no advantage. And really, if we're talking about McDonald's replacing employees with iPads then there's a hundred reasons why the iPad is better, especially in concert with a machine making the food.

But here's a robot you might not have thought of, the robot that already does the inventory, ordering, pricing, labeling, and a million other retail tasks so that the Gap employee can be folding clothes: the cash register. When you bought something back in time a few decades, someone actually had to write that down or, more commonly, guess what was sold by how much money they took in and the understanding of their store sales. It is amazing now that most retail sales jobs essentially amount to making the sales floor presentable and customer service actions. These are also amazing machinery involved efficiency gains, and are mainly the type we will see in the future. Think of accounting and payroll and how many other jobs are already automated that we don't even have the wherewithal to understand, and you begin to see the scope of the transformation already in place. Another symptom of this is income inequality.

The real problem is that eventually we will move past an economy where it is no longer possible for enough people to find work at all to support any kind of economy. The capital owners will literally own too much of the wealth. At that point society as a whole will have to completely change and abandon capitalism for some hybrid of socialism. Not to say that the government should own the means of production, but that we would basically all get some minimum share of the GDP in order to make the world work. There's no way around it.