NMR Quantum Computation: a Critical Evaluation
  Liquid state nuclear magnetic resonance (NMR) techniques have produced some spectacular successes in the construction of small quantum computers, and NMR is currently by far the leading technology for quantum computation. There are, however, a number of significant problems with any attempt to scale up the technology to produce computers of any useful size. While it is probable that some of these will be successfully sidestepped during the next few years, it is unlikely that they will all be solved; thus current liquid state NMR techniques are unlikely to provide a viable technology for practical quantum computation. 
J. A. Jones