I'm a user of dropbox. The way it works is they provide a client for Windows/OSX/Linux which monitors a "Dropbox" directory. When you add/change/delete a file in that directory tree it will be synced with your dropbox account and any other subscriber you
have to your account. Not only that, for the Free user it keeps a history of file changes for 30 days so you can un-delete something or get back changes you lost by accident. For the pro users you can make this permanent history.
I have a client for my iPhone and iPad as well (Taking photo's via iPhone and your pictures can instantly appear on your subscribed machines.)
I currently have 50gb of storage with them and share some folders with friends and colleagues, makes things so much easier especially as one uses Linux and another uses a Mac.