I love using matcap in solid view. I learned about this function while working through Johnathan Williamson’s  hard surface modeling videos at CGCookie.com. Mesh modeling the head is proving to be a challenge and I found using the matcap in while in solid view I can very easily spot strange deformations in the mesh and at the same time have another view port open in edit mode pushing and pulling verities while watching the deformations disappear. Such a helpful tool for me to use and I had know idea what it was for previous to those videos. Here is a shot of where I am at so far.