You can observe a lot by just watchin' (attributed to Yogi Berra).
Some social scientists will do any mad thing rather than study men at first-hand in their natural surroundings (attributed to George Homans).
Observations of research subjects may be done by non-participant observers, those who spend time among research subjects only to collect observations but do not significantly interact with subjects. For example, one may observe a classroom, an encounter between doctor and patient, or the way people use public parks. On the other hand, some observations are enhanced by participating in the daily lives of those being observed-"participant observation." This is often done as a part of long-term ethnography (usually considered its sine qua non). But participant observation may be done as part of shorter, more directed ethnography, such as that of a fishing boat by Gatewood (1985). However, it is not a method that may be taken on frivolously and briefly. A good deal of time and rapport-building is usually necessary before informants stop noticing the novelty of the researcher's presence and participation, and go about their daily routine as they would normally. And one must attend to the ethics of gathering and possessing information about the daily activities of people who may have come to think of the participant observer as more of a participant than an observer, with the attendant level of confidence that produces.
References:
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Anderson, E. (1990). Streetwise: Race, Class, and Change in an Urban Community. Chicago: University of Chicago Press.
Davis, F. (1980). The Cabdriver and his Fare: Facets of a Fleeting Relationship. In L. Coser (Ed.), The Pleasures of Sociology (pp. 515). New York: New American Library.
Fine, G. A., & Sandstrom, K. L. (1988). Knowing Children: Participant Observation with Minors. Thousand Oaks, CA: Sage.
Humphreys, L. (1970). Tearoom Trade: Impersonal Sex in Public Places. Chicago: Aldine.
Levine, H. G., Gallimore, R., Weisner, T. S., & Turner, J. L. (1980). Teaching Participant-Observation Research Methods: A Skills-Building Approach. Anthropology and Education Quarterly, 11(1), 38-54.
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Spradley, J. P. (1980). Participant Observation. New York: Holt, Rinehart and Winston.
Webb, E. J., Campbell, D. T., Schwartz, R. D., Sechrest, L., & Grove, J. (1981). Nonreactive Measures in the Social Sciences. Boston: Houghton Mifflin.
Williams, T. (1992). Crackhouse: Notes from the End of the Line. Reading, MA: Addison-Wesley.