I recently went to a make-up class for the session I missed: using flash with ambient light. For the rest of the course we had focused solely on shooting with strobes, but for this one session we learned how to capture part of the image with the strobes and the rest with ambient light.
We set up two mannequins, one against a black background with a halogen light shining on it, and the other in the foreground only illuminated with two strobes. We metered the strobes and then took our first picture at sync speed, but this captured only the foreground. We then adjusted the shutter so the halogen-lit background would be exposed correctly.
After figuring out how to capture both the background and foreground, we added party wigs to the mannequins in order to try to freeze motion with the flash while having motion blur in the ambient-lit portion of the image. Check out the album to see the results.