[darkFunction]

The problem with smart contracts is that of defining trustless "oracles", or, how do you get data in and out of the network without relying on vulnerable points of centralisation. As soon as you require information about something other than the internal state of the chain, you have a problem. I believe some companies are attempting to implement solutions at the moment but I'm not familiar with the technology.

Crowd-funding is an already popular use case for blockchain contracts, as well as the creation of tradable tokens built on top of the platform. Decentralised exchanges are a nice idea but to my knowledge they are outclassed by the speed of centralised servers. Decentralised, "fair" casinos (such as Edgeless) are also possible with smart contracts but I think they won't be able to compete with traditional casinos that have an edge but offer large and enticing welcome bonuses.

For a quick overview of some of Ethereum's Dapps you can look at: http://dapps.ethercasts.com/