Dates and views. Command-T jumps to today, Shift-Command-T opens a date picker, and Command-1 through Command-4 switch between Day, Week, Month, and Year view.
Events. Command-N adds an event, Command-E edits the selected one, and Option-Command-I opens it in the inspector window for a closer look.
Moving an event with the keyboard. With an event selected, Control-Option-Up Arrow and Control-Option-Down Arrow move it earlier or later; the step is 15 minutes in Day or Week view and a week in Month view.
Calendar list. Space toggles the selected calendar's checkbox when the calendar list is open, and Command-click any checkbox to show or hide every calendar at once.
Full screen. Control-Command-F enters full-screen view; Escape exits it, and also closes an open event editor.