Site testing data provides an essential part of the justification for funding any new astronomical facility by defining the technological design and determining the telescope performance, thus allowing the scientific objectives to be prioritised. Here we review the current status of site testing at Dome C by examining the range of instruments that have been, or are planned to be, deployed to the site. We then investigate in more detail preliminary data which has so far proven crucial for telescope design, data for which discrepancies exist between two or more instruments, and required data for which there are no current plans to obtain. We discuss the implications of this data on the technical design, expected performance, and the scientific capabilities for a 2.5 m class optical/infrared telescope. Finally, we identify the site parameters that require further study, and define the experiments necessary to determine these parameters.