I have seen them used to launch cars long distances. See the related link for an example from YouTube. If you want me to come up with new ideas, well, that's your job :)
1. Temperature below zero
2. Earning money is positive, owing it is negative
3. Fractions can be represented as negative exponents.
4. To take dollars off a price, i.e. a discount.
5. When talking...
Yes. If you count Hitler as a leader that is. Many people saw him as a leader and since they were considered his "followers" he had power over the people, and the army too (I think). Basically Hitler...