I was working the last three days with Live Mesh, which is currently in beta now, and it is definitely a great tool for sharing and synchronizing files and working on different devices. Since it is still a beta, the number of different platforms and supported devices is still limited (XP, Vista 32bit, Vista 64bit, OS >=10.5.1) but this will change once this product is officially released. Even if it is in beta, it worked perfectly stable. (Here's a quick description).
With Live Mesh Microsoft offers you 5 GB webspace for free. Here some screenshots: