I'm less concerned about AI "taking our jobs" (see the other comments on lump of labor fallacy, etc) than what happens if we cure all disease, which is the only thing keeping population in check. How many humans can Earth support? What happens when we run out of resources? Will the ability for humans to live much longer help us colonize space? I hope so.

That said, it would be really nice to cure diseases that are particularly painful or kill young people (cancer, etc).