Live Mesh is a data synchronization system from Microsoft that allows 5GB of files, folders and other data to be shared and synchronized across multiple devices.
Once a folder is set for synchronization, it will be available in all devices, and any changes made to the content of the folder will be reflected across all devices. Live Mesh uses FeedSync to convey the changes made in each device so that the changes can be synchronized. The information about devices and folders participating in a synchronization relationship is not stored locally but at the service-end. Devices in a sync relationship are collectively referred to as a Mesh.
Been using this a few days now - keeping a folder sync'd on my work PC, home laptop and iPod. The process appears to be simple, uncluttered and intuitive and hasn't yet made me want to kill anyone, which may mean that it's objectively the best app Microsoft have ever released.