Some may not like what I have to say about quantum computing, but so what.  You, Macadonian, may like what I have to say, since after reading my explanation below the simplest conclusion is that bitcoin has nothing to worry about as regards to quantum computing.

And so, here is my brief rant on quantum computing.

After having studied quantum mechanics for a long time I have found that all of those quirks or what they like to call "quantum weirdness", isn't weirdness at all but rather its the limitations of our devices that produce the illusions of weirdness.  All of the technology that has been used in the experiments to study quantum effects suffer from the problem that they are large gross machines compared to the tiny things we are trying to observe.  That is, our machines are crude, and they are taken to the limits of its properties to try and take measurements of stuff that is much smaller than the equipment at hand.  It is our crude observations which end up with what appears to be quantum weirdness.

In more recent experiments it gets continuously shown that things at that level actually behave in a "classical" sense, but appear to produce a more complex emergent behavior.  It is this complex emergent behavior which then gets labeled quantum weirdness.

And so, when it comes to building computing machines that will take advantage of this quantum wierdness, the actual devices will simply be employing a complex emergent classical property.  That is, the quantum computers will just be very advanced, very fast classical computer versions of what we have today. (can you see how I can find this topic of quantum computing to be rather silly).

If you are worried that a quantum computer can cause a collision with a bitcoin private key (like finding a key with someone's bitcoin), sure it could be possible.  But I do like reading about what an incredible machine it would take to do this.  Here is a great thread on this topic:
https://bitcointalk.org/index.php?topic=5147514.msg51224295#msg51224295

Essentially they describe how if someone where to build a big enough computer to crack bitcoin in 2 minutes, say, maybe with a large "quantum computer", the bitcoin code can be upgraded to then make it near impossible again for that new machine to crack it.  The code can always stay ahead of the hardware.