The biggest obstacle to quantum computing to date is what is known as decoherence, "or the tendency of a quantum computer to decay from a given quantum state into an incoherent state as it interacts, or entangles, with the state of the environment."  Unfortunately, interactions between qubits and their environment are impossible to prevent, and what is worse, is that these very interactions can easily corrupt the data stored in a quantum computer.  Fortunately, theories like entanglement are beginning to provide solutions for the problem of quantum error correction. 

 
(c)source

                                     "... I think I can safely say that nobody understands Quantum Mechanics"                                    -Richard Feynman

Right now, were are aware of only a small fraction of the applications of quantum computing.  The next step, is to construct devices which will enable us to test out our theories by actually performing quantum computation.  Only recently, through the use of nuclear magnetic resonance, scientists from the Los Alamos National Laboratory and MIT have produced the first examples of quantum computing.  Now, key research must take place to counteract the effects of decoherence and overcome other daunting obstacles to reveal the true power of quantum computing.

Bibliography