Dropbox is a new service (I believe it is still in beta) which provides a method that requires little to no effort to keep files on your desktop or laptop synced with other computers.
Without going into a lot of detail, DropBox is essentially a folder on your machine (PC or Mac). You can then add additional folders and files to the DropBox folder and any changes that you make (add, edit, copy, delete, rename, etc) will automatically be synced to the DropBox server.
Rather than doing a very poor description of what DropBix can do, view the screencast here about the produvt. And thanks to Phil Read for pointing out this service to me.