When I was in flight school, I went through trainning with a partner. When we were working on our commercial tickets, we would both fly and log it as PIC. How you ask? One would wear some sort of view limiting device and the guy in the right seat would fly visually. Now we could only do this in VFR conditions. If it were IMC, then only one of us would log the flight as PIC. Just my 2 cents..