I will review the basic techniques and ideas involved in the study of dualities in D=3,N=4 supersymmetric gauge theories using partition functions on a sphere and demonstrate how these partition functions can provide an extremely non-trivial check of mirror symmetry for a large class of quiver gauge theories. In particular, I will focus on theories whose Type IIB descriptions involve D3 branes ending on orbifold/orientifold 5-planes. In addition to providing a convincing check, this procedure allows one to extract important information about the duality like the "mirror map" rather trivially.