My kids are constantly dropping food and untensils! If it is a dry food, like a chip or cracker, I usually let it slide, or maybe attempt a quick brush off. My husband says there is scientific evidence to back up the 30-second rule, and I hate wasting food. If it is a piece of meat or fruit, I wash it off or have them wash it off before eating it.
If we had a pet, I suppose he or she would save us the trouble. But in any case, I rarely throw food away. We cannot afford the waste.