Clearly both surveys and focus groups are important tools for gathering information about a particular population.  Usually surveys are used first, to a get general sense of the population.  Surveys are then followed by focus groups that get more in depth information.

However a case can be made for reversing this order and starting with focus groups first, followed by surveys (see: “Use of Focus Groups in Survey Item Development“, The Qualitative Report, Nassar and Borders, March, 2002).  Focus groups can often help to define survey questions or inform how questions are phrased.  This can be particularly important for technology surveys, helping to couch questions in terms that those surveyed can understand.