Android app + machine that mixes drinks. As Paul Krugman notes in his “futurism article“, most things that symbolic analysts do can and will be automated. Add to that category (unsurprisingly) repetitive remedial tasks. This, of course, reduces the marginal product of bartenders to zero for people who eschew witty banter and simply want a drink. On the plus side, you would never have to ask a bartender if he knows how to make a particular drink (I’m not creative with drinks…).
However here is a developing point; In any society, people should be able to dream up jobs for other people to do (for example, at one point in history, ironing newspapers was someone’s job). In reality, that may require some changing mores about what is considered paid work. The second part of this point is that I think as specific human interactions become more rare, they become more premium, that is, the marginal product of simply being human and having a particular skill rises (and if economics is any guide, extremely rapidly). That doesn’t bode well for the quantity of jobs, but it does for the quality of reproduction.
Keep in mind, however, that up to this point society has seen it fit to heavily subsidize areas of the economy which have already suffered from this phenomenon (arts, music, farming).
P.S. I think that the future will see the rise of complementary currencies — money with different mechanics than legal tender — which will facilitate this type of human interaction. I think a lot of economists overlook this possibility in their futurist extrapolations. Many try and shoehorn the current rules into their interpretations…but I think that kind of brushes aside fundamental concept in economics: incentives.