  In this note we review recent progress about fluctuation relations and their
applicability to free energy recovery in single molecule experiments. We
underline the importance of the operational definition for the mechanical work
and the non-invariance of fluctuation relations under Galilean transformations,
both aspects currently amenable to experimental test. Finally we describe a
generalization of the Crooks fluctuation relation useful to recover free
energies of partially equilibrated states and thermodynamic branches.
