NLS user since 2000
The panel nature of this data set is wonderful. Having information on individuals over time is useful for accurately determining the role of causal influences on behavior as distinct from correlation. It also allows for the analysis of dynamic behaviors, which encompass just about everything that we do. I am currently examining the role of body mass on wages through the lifecycle channels of education, employment, marriage, and children.
Very few nationally representative datasets have information on individuals for 20+ years. NLSY, for example, has very detailed education, employment, marriage, and children information.