Yes sorry i mean lightmaps. It's not a built-in feature yet (afaik) but there are several scripts in the forum and in the wiki to use an ingame lightmapper and someone is currently creating a BSP creating tool with lightmap support:

http://forum.unity3d.com/viewtopic.php?t=35498

The decal system you mean uses a texture projector to project blob shadows for example.

And you can always bake your shadows in a model tool too if you know the lightning settings for your scene. Of course it's more work but well, it's the free version of Unity.