Just to complement the earlier post, here are some facts about this voxelization method.
Here you can see the Standford dragon after voxelization in a 128x128x128 grid:
The original model has 260,000 triangles. The resulting mesh resolution for 128x128x128 is much lower, so a lot of detail is necessarily lost. Still the voxelization preserves the key features of the model.
This runs in 14 milliseconds on an ATI 4770.