  The CSCW community has a history of designing, implementing, and evaluating
novel social interactions in technology, but the process requires significant
technical effort for uncertain value. We discuss the opportunities and
applications of "piggyback prototyping", building and evaluating new ideas for
social computing on top of existing ones, expanding on its potential to
contribute design recommendations. Drawing on about 50 papers which use the
method, we critically examine the intellectual and technical benefits it
provides, such as ecological validity and leveraging well-tested features, as
well as research-product and ethical tensions it imposes, such as limits to
customization and violation of participant privacy. We discuss considerations
for future researchers deciding whether to use piggyback prototyping and point
to new research agendas which can reduce the burden of implementing the method.
