A few years ago I worked on Tim Burton's Dark Shadows at MPC. We created a full CG face for Eva Green's character Angelique.
Angelique had a fight with Johnny Depp's character Barnabas Collins, and her face and upper body gets destroyed during the action.

In that case, all the broken parts where painted by hand as texture masks, and then the FX team generated 3D geometry and simulations based on those maps, using them as guides.

Recently I had to do a similar effect, but in this particular case, the work didn't require hand painting textures for the broken pieces, just random cracks here and there.
I did some research about how to create this quickly and easily, and found out that Modo's shatter command was probably the best way to go.

This is how I achieve the effect in no time.

First of all, let's have a look to Angelique, played by Eva Green.

Once in Modo, import the geometry. The only requirement to use this tool is that the geometry has to be closed. You can close the geometry quick and dirty, this is just to create the broken pieces, later on you can remove all the unwanted faces.

I already painted texture maps for this character. I have a good UV layout as you can see here. This breaking tool is going to generate additional faces, adding new uv coordinates. But the existing UV's will remain as they are.

In the setup tab you will find the Shatter&Command tool.
Apply for example uniform type.

There are some cool options like number of broken pieces, etc.
Modo will create a material for all the interior pieces that are going to be generated. So cool.

Here you can see all the broken pieces generated in no time.

I'm going to scale down all the pieces in order to create a tiny gap between them. Now I can see them easily.

In this particular case (as we did with Angelique) I don't need the interior faces at all. I can easily select all of them using the material that Modo generated automatically.
Once selected all the faces just delete them.

If I check the UVs, they seem to be perfectly fine. I can see some weird stuff that is caused by the fact that I quickly closed the mesh. But I don't worry at all about, I would never see these faces.

I'm going to start again from scratch.
The uniform type is very quick to generate, but all the pieces are very similar in scale.
In this case I'm going to use the cluster type. It will generate more random pieces, creating nicer results.

As you can see, it looks a bit better now.

Now I'd like to generate local damage in one of the broken areas. Let's say that a bullet hits the piece and it falls apart.
Select the fragment and apply another shatter command. In this case I'm using cluster type.

Select all the small pieces and disable the gravity parameter under dynamics tab.
Also set the collision set to mesh.

I placed an sphere on top of the fragments. Then activated it's rigid body component. With the gravity force activated by default, the sphere will hit the fragments creating a nice effect.
Play with the collision options of the fragments to get different results.