For a very quick way to add a 3d effect on any text or shape, all we need to do is duplicate and shift.
Start with your base graphic. In our case we went with a simple Pintrest lookalike logo.
Duplicate the graphic you want to create, color it white, and move that layer behind the main graphic.
All you need to do is move the duplicate layer directly underneath the main graphic, and then move it 2px to the right, and 2px down, and the 3d effect is done. Here is the finished effect.
If you have updated to Pixelmator 2.2 Blueberry, you can use the new shape styles to create the same effect above very quickly. Create your text or graphic, convert it to a Shape, and in the Shape Styles window, select the Inner Shadow setting, and play around with the colour, size, and angle of the inner shadow.