I love keyboard shortcuts, but I must admit there was a time when they seemed not that much more efficient than just using my mouse. But, once they had been properly drilled into my head at school, they have saved countless seconds of design time. Of all the shortcuts out there command + z is my favourite. If I had a Commands poster it would say "Just ⌘Z it!"
These great posters are from designer Christopher David Ryan. Check out his website My Little Underground where you can purchase his Commands prints.