I am flying SFO-SYD next month in C and decided to use a SWU to move to first (hoping for a marginally better night sleep as I have to get off the plane and start working) - business is nearly full with few open seats and had no problem using SWU to first just a few days ago - there was only 1 other person up there before I upgraded. Perhaps few are seeing the need to pay more for first since it sounds like its only a marginal improvement over the lie-flat business seats.