For the foreseeable future, quantum computers will only be used in those situations where a classical computer does not work at all. Even in cases where one utilizes quantum computing, the quantum computer will work hand-in-hand with a classical computer to find the total solution. As an example, Shor’s algorithm for factoring numbers is broken down into two parts. The first part of the algorithm which would be performed on the classical computer turns the factoring problem into a problem of finding the period of a function. The second part uses the quantum computer to implement a quantum Fourier transfer (QFT) to find the period which is much, much faster than the classical fast Fourier transform (FFT).
So don’t expect anyone to miniaturize a dilution refrigerator so it can fit into your pocket. Due to the demons of decoherence quantum computers will be large and bulky in order to provide the necessary shielding of light, heat, magnetic waves, electromechanical emissions, and anything else which might cause a qubit to collapse. This alone, this will relegate quantum computers to data centers or in the cloud where they will be used to solve really difficult computationally intensive problems.