Right now it hasn't amounted to anything useful, other than Shor's and 'experiments' and promises and applications that are no better done on a GPU rack right now.
Shor's paper on polynomial time factoring is from 1997, first real demonstration of quantum hardware (Monroe et al.) is from 1995: Yes, quantum has had decades -- but only barely, and is has certainly only now started to have generations.
To look at the kind of progress this means, take a look of some of the recent phd spinouts of leading research groups (Oxford Ionics etc.): There are a lot of organisations with nothing but engineering to go before they reach fault tolerance.
When I came back to quantum three years ago, fault tolerance was still to be based on the surface code ideas that floated when I did my phd ('04). Today, after everyone has started looking harder, it turns out that a bit of long-range connectivity can cut the error correction overhead by orders of magnitude (see recent public posts by IBM Quantum): The goalposts for fault tolerance are moving in the right direction.
And this is the key thing about quantum computing: you need error correction, and you need to do it with the same error-prone hardware that you correct for. There is a threshold hardware quality that will let you do this at a reasonable overhead, and before you reach this threshold all you have is a fancy random number generator.
But yes, feel free to be a pessimist -- just remember to own it when quantum happens in a few years.
The current emphasis on NISQ systems is a bit of a desperate measure because the most we can get out of such systems is evidence that quantum computing can work in theory; they do not advance us towards having a workable quantum computer.
The last paper I saw posted on hackernews from Gil Kalai included a few explicit predictions about what would be impossible in quantum error correction.
This was a paper from a few years back.
The problem is that now Google has published results which imply that some Kalai's predictions turned out false.
The paper in question is Google's recent "below threshold"/"beyond break-even" QEC paper. I believe Kalai was predicting below threshold QEC to be impossible IIRC, among other things.
Not sure if Kalai has responded or updated his predictions, I haven't been following him closely.
1) While quantum computers are potentially exponentially faster, they also seem to be exponentially more expensive given the number of qubits, so you actually can't save money by building a huge quantum computer. This may or may not change in future. Also, there was a problem with error correction, which is made much harder by the nature of quantum computing. Smart people are working on that, I don't know the current state of progress.
2) Despite the hype, only some problems can be calculated exponentially faster using a quantum computer, not all of them. This is analogical to parallel computing: having two CPUs instead of one will allow you to calculate some things twice as fast, but some other things will require exactly the same amount of time because their steps need to be done sequentially. Similarly, a quantum computer is like a network of billions of computers that are spread across the multiverse, but they need to all run the same code, and to compress the results of the gigantic computation into about dozen bytes. So it's great for highly parallelizable tasks where the entire required output is a "yes or no" or a single number... and less useful for everything else. That still includes some important scientific problems, such as simulating atoms and molecules. But those are not the things we typically use computers for.
In some ways it is similar to fusion. People have been working on it for a long time. The benefits are potentially significant (shor is cute and all but really the big deal would be a cheap way to simulate other quantum systems) but the challenges are also significant. Real progress is being. Things that were super challanging 10 years ago are solved now. The field is advancing. But we still have a long way to go.
It is not a scam itself, but a lot of scammers use the language of quantum to sell their scams. You should treat anyone convincing you that they will have a useful quantum computer in the next 5 years the same way as someone offering you a fusion reactor (i.e. full of shit).
Its still a worthwhile pursuit, even just as a physics experiment. It pushes the "weirdness" of quantum physics to the limit - by literally disproving the extended church turing thesis. If we make a real quantum computer - that is proof that quantum physics is really how are world works. Its not just something else that is being misinterpreted.
The next big challenge will be mounting the controlling hardware, currently connected via coaxial cables, onto the chip while preventing the introduction of new sources of interference so that error correction can run. That will take a miracle.
Of course, an alternative is a million coaxial cables connected to a chip cooled close to mK temperatures.
Decades is a short amount of time in human history. Many things took centuries to invent.
The silicon valley approach of a year or two of runway is how apps are built, but that's not how science is built.