We just finished this 30 second spot for sexual education in New Zealand. The characters are 2D (except for the live action ones). The environments are all 3D.
small version (1.5 meg quicktime):
larger version (5 megs quicktime):
some highres images:
We rendered out the environments to RPF format, which transferred over the camera data to combustion, so we could position the 2D characters in the 3D space. We then used combustion to shade the characters, & create the rimlighting. Let us know what you think!