This contract keeps user's ethers in its internal storage. This approach allows cheaper batch transfers than series of individual Ethereum transactions.
I would like to get any feedback from more experienced contract designers than me.
The code is on GitHub (you can add inline comments there):https://github.com/chfast/contracts/commit/61b331ebd79f7ccfcf7aff6d64c73113d577d45f
or in solidity-browser:https://chriseth.github.io/browser-solidity/?gist=ac140b941584ca36be92
I'm thinking of using Serpent later. I was told it gives you more control over EVM code and therefore better optimizations possibilities.