Suppose I wanted to create a "game" running on Etherium's global computer; perhaps one that allowed people to own and breed virtual cats. I might want a random component in my "breed" behavior.

Imagine I want to create a smart contract where tasks are created by customers and assigned randomly to "turks" who submit completed tasks and are paid (if the task is accepted). A random number might be one useful part of the task assignment process.

ANY program that would random numbers is a potential candidate.

It's pretty much the same use case as any standard code, smart contracts are just decentralised code after all.

Gambling is pretty much the only use for smart contracts in general.