I ask because yesterday I shot an event where bouncing was nearly impossible. The ceiling was dark AND there were these large, dark "partitions" hanging down about 3-4 ft from the high ceiling, effectively creating pockets for the light to be trapped in. Walls were brick or painted dark too. Natural lighting was all over the place - from the daylight spilling in floor to ceiling windows at one end, to dark red "club" lighting only 30ft away on the other side of the room.
Having said all of that, I did bouce my flash behind me (although what the light was reflecting off of, I'll never know) and got ok pics. Most needed to be pushed in post and the WB was way off, but I shot RAW so no worries.
So, what do you do when bouncing is not a viable option?