Dropbox automatically syncs files online and across computers. The service integrates perfectly with native operating system file managers (Explorer on Windows, Finder on Macintosh). Every file in the Dropbox directory is stored on every device connected to the Dropbox account.
The synchronization process is generally very quick (though larger files require more time to upload to the Dropbox servers).
Files and folders can be shared with other Dropbox users, and it is possible to create public links for sharing files publicly via a web URL. Publicly shared photo directories can be automatically presented in slide show format in a web browser.
ZumoDrive uses a different model of data storage. Files are stored online, and files can be accessed from any device connected to the ZumoDrive account. Files are downloaded as they are requested, and files can be cached for offline access.
ZumoDrive files are stored in a separate drive on the guest operating system (Windows or Macintosh). While local storage is maximized by streaming and opening files directly from directories stored online, performance is somewhat decreased (this is particularly noticeable with large files).
ZumoDrive also enables file sharing and instant photo albums, much like Dropbox.
Both ZumoDrive and Dropbox are useful tools for accessing files on multiple devices. They permit a useful combination of web storage and local applications. Traditional web applications (such as Google Apps) tend to lock data into proprietary formats.
Dropbox and ZumoDrive enable users to maintain traditional file system interactions with files and directories while embracing advantages of web-based backup and content distribution. Both have free entry-level accounts.