Pixelmator is a great Photo Editing tool for Mac. However of the important function like Exporting the image to PNG, JPEG etc. is not accessible via a shortcode. This is required specially when you one to just use keyboard without the track pad to edit and export images.
So we can use MacOSX to create a shortcut for us here.
1) Close the Pixelmator app
2) Open System Preferences (from dock or spotlight) and click the Keyboard icon to go the Keyboard settings section.
3) Click on the Keyboard Shortcuts tab on the top
4) Select Application Shortcuts item from the left panel.
5) Click on the rectangular + button to add the shortcut.<!>
6) Select the app name as Pixelmator from the application drop down.
7) Type is Export... as the Menu Title
8) Finally assign the shortcut key that you want to use. say Command + E . Click on Add button to save it.
Now launch Pixelmator and click on the File menu and you should see the shortcut for Export function is there. Go ahead and use it, sure this would make your life easier till this is part of Pixelmator itself sometime in future.