A central concept in computing these days is syncing between the myriad of devices and storage locations that a user might own. The reason why this is a good idea is because users want to get away from the problem of having to keep track of where data lives. They simply want the information that they need to be available at their fingertips. I have been using Foldershare for a number of years, which was acquired by Microsoft. Now based on the same technology, Microsoft have released a new service called Live Mesh, which syncs not just folders and files, but also applications. These types of services are also being developed by startups in the valley, including SugarSync, which I beta'ed, and also Dropbox.
Of these, only Foldershare and SugarSync currently support the Mac.
I believe this is an important step forward for end-users, as this relieves them from having to worry about where the data is located, and they can simply rely on the background services to make the data available. This is the concept of content-based computing and networking, which Van Jacobson here at PARC has talked about.