I use the Microsoft solution as I have found that it very nicely keeps my documents in sync between two Windows PCs and a Mac. It has a relatively easy online interface that lets you view what is in your cloud and download from. It is currently called Windows Live Mesh. As far as safety, I figure it is as safe as any other information I have up in remote servers somewhere (email with Gmail/Google, contacts with MobileMe/Apple, etc.). You install an app on your computer and it runs in the background and keeps files/folders you select in sync between your machines and the cloud.