Lightmapping question.

I'm testing the Unity built-in lightmapper(reading this: http://unity3d.com/support/documentation/Manual/Lightmapping.html) and get some strange artifacts.

It only happens when I turn on Soft Shadows(in Lightmapping/Object/Baked Shadows, with the scene light selected). So why do I get the strange stripes and artifacts on the eges and what can be done to fix it? And it seems strange that some cubes are baked correctly, while the others are not. Why?

Your problem is that the UV map of the cube : I think they are not properly unwrapped (see : http://en.wikipedia.org/wiki/UV_mapping). I don't think you can unwrap in Unity so I advise you to import a cube properly unwrapped from any 3D software (Blender, Maya, 3DS).