This paper reports the findings from research which explored decision making and practices underpinning the implementation or non-adoption of social media in archives and libraries worldwide. Archives and libraries continue to face demands, whether from senior management, funding agencies, the government, or taxpayers to demonstrate accountability. Evaluation provides evidence to meet such demands and to gain, validate, or sustain support for programs and activities. Being able to show success is a key step for archives and libraries that need to rationalize or win support for the continuance of their social media efforts. Related to this are questions about whether or not there should be a preservation strategy for the content of social media as well as a plan for sustainability of infrastructure to support these activities. Our survey findings suggest that archives and libraries know that they are not necessarily choosing the evaluation methods that can best demonstrate the achievement of their intentions, and furthermore that they lack strategies and policies for preservation and sustainability.