Most of the operations in Blue Pencil provide native undo/redo support by leveraging Maya's undo stack. This includes strokes created with the pencil, brush and eraser tools, inserting and removing keys, cut, copy and paste operations, and the retiming tool.
To undo an operation, press 'Z' or select Undo from the main menu (Edit->Undo).
To redo an operation, press 'Shift+Z' or select Redo from the main menu (Edit->Redo).
*Hotkeys may vary