Calendar Shortcuts
Cmd/Ctrl + Click: Select an event. Selection is persisted through calendar navigation, so you can select events in a particular month or week, navigate forward, and select again to add to your selection.
Cmd/Ctrl + A: Select all visible events. This shortcut also respects filters, so you can quickly select everything with a particular tag by filtering by that tag, and then selecting all.
With events selected
Cmd/Ctrl + M - Move selected events
Cmd/Ctrl + D - Duplicate selected events
Cmd/Ctrl + E - Edit selected events
Cmd/Ctrl + Delete/Backspace - Delete selected events
Esc - Deselect all selected events
In the bulk action palette
Up & Down Arrow Keys, Tab & Shift + Tab - Navigate the list of actions
Return - Execute the chosen action
Esc - Close the bulk action palette without saving
Editor Shortcuts
Esc or Enter/Return - Close the editor without saving changes.
Tab - Next info field
Resource Fields (Locations, People, Etc.)
You can add resources quickly when creating events by typing to search, pressing Tab to move to the first option in the list, Space to select that option, then Shift + Tab to move back to the search bar. The text in the search bar is already selected at that point, so you can just start typing again.
Note: For Safari users, the Tab key will take you to the next set of fields (Status) intead of through the options in the resource list. This functionality is built into the browser.