Dr. Tina Basi sums up three different kinds of research categories quite simply and nicely over at the Experentia blog.
From her presentation:
Quantitative data, and surveys are useful for learning about numbers, stats, trends, and retrospective information.
Focus groups are good for learning about attitudes, perceptions, discourse, and social climates. Ethnography about building up a rapport, seeing things that people cannot articulate.
Ethnography examines everyday practices, real life contexts, and living situations that you can not explore or understand with other methods.