This article provides a balanced and thorough discussion of the use of focus groups as both a formative and cumulative form of usability evaluation and/or as part of a user-centered design process. The article highlights many of the potential advantages and disadvantages of focus groups. Probably the biggest risk in terms of focus groups is the cost involved, in terms of time, money and effort. As the article states, if a focus group is not well-run, it can end up being dominated by a few individuals and the opinions expressed may not reflect the true group consensus.
Focus groups are probably most useful to evaluate and discuss prototypes throughout the design process. Particularly in the context of a mobile environment, it is important to provide users with some prototypes, whether low-fidelity paper prototypes, or even flash demos to facilitate discussion of design ideas. The article provides a thoughtful discussion of the issues surrounding focus groups and would be a useful read for anyone considering using a focus group as part of their design or evaluation process.