The most commonly described paradigm for quantum computation involves switching individual qubit-qubit interactions 'on' and 'off' at will. This is of course an enormous challenge for many of the proposed experimental implementations. I will discuss alternative models that may allow one to (a) give up all local manipulations in favour of global control, (b) leave the underlying physical interactions on continuously, or (c) both.
Related papers: quant-ph/0407063 Phys. Rev. Lett. 90, 247901 (2003). Phys. Rev. Lett. 88, 017904 (2002).