Quantum computers don't yet exist as far as we know.

But, one of those tasks this guy is talking about that is well suited to quantum computers is breaking encryption. NSA anyone? Things like 256bit encryption is today considered VERY secure as it would take a modern super computer longer than the age of the universe to crack. But a quantum computer could do it relatively quickly.

Some very fast, very complex calculations, but not very useful for data storage or anything.

It's much less useful than even that. For standard computers even for the CPU it's useless. It's only useful for some very specific scientific tasks like breaking encryption, weather modelling and other types of scientific models of the real world. For every day use it's actually slower than a regular computer. But for these few tasks it's MILLIONS of times faster!