That may explain the several million users of Dropbox, a startup service which gives away more storage than Google, up to two gigabytes. Dropbox offers a magic folder on your desktop that looks and acts the same as any other, except for this: it's being watched. Move items into the folder, create new folders, open and modify documents, and a tiny piece of Dropbox monitoring software replicates those actions on every other computer to which you've linked your account. The company also stores a copy of the file for access from the Web, and archives older revisions for ready retrieval. This back-up capability can be ignored; it requires no scheduling or configuration. Dropbox restrains size and bandwidth by storing differences in updated files. And there's another bit of magic that's helped Dropbox go viral: any folder in your Dropbox directory can be shared with other parties, and any changes are immediately synced for both parties.