It sounds strange to talk about a shell, when you are talking about OSX. It is not linux is it? But having come from linux, at least for me, many things are just faster from the shell. And combine an always running terminal with quicksilver and you are typing in the blink of an eye. And why zsh? Well, not all shells are created equally. One shell rules them all… Anyway, it has way more shortcuts and other goodies then any other shell.