I think the following viewpoint has been interesting. If we look back at the development of the electronic computer, it's hard to say there was a single point it "delivered". Was it the Atanasoff–Berry Computer, the Collosus, the ENIAC (1940s)? Each of these miss some things that we commonly think of as a modern, generally useful computer. (Lacking programmability, Turing completeness, or stored program representation, respectively.) Do we have to wait all the way until, say, Apple II (1977) was released to consider delivery?

I don't have an answer myself, but it seems to most people, "delivery" doesn't mean "when it's useful", but rather "when it's usable, useful, and generally available for use."

If we use that as a benchmark, quantum computing has definitely hit "usable". It is teetering on "useful". And the beginnings of "generally available for use" have been explored by a few industrial players [0, 1].

[0] Rigetti Computing's Forest: http://forest.rigetti.com/

[1] IBM Research's Quantum Experience: http://www.research.ibm.com/quantum/