I tried to work on two layers simultaneously, and apparently it is impossible... ? I just can't figure out how to apply anything to two (or more) layers without doing it individually! For example, I wanted to erase things on two layers at once... Selecting two layers at the same time (shift or ctrl-click) makes nothing but the move tool work. Linking two layers does absolutely nothing except allow me to move two layers together. In order to use a tool like the brush, I have to select one of the linked layers, and the effect of that tool only applies to the active layer and not both.
Am I missing something or is this just impossible with PS?