Six ways that I use Dropbox:

1. Worry Free Backup.  Because Dropbox is continually running on my computer, I know that any files that I save into it are instantly backed up securely to Dropbox's servers.  If my hard drive were to crash today, I would be able to easily retreive my files, even those I worked on this morning.
2. Restoring Previous Versions.  Anything in the Dropbox folder can be restored to a previous version, even if you deleted the file.  While I don't use this feature very often, the times that I have used it have saved hours of rework.
3. Public File Sharing.  Whenever I have to send a large attachment in an email, instead of worrying if the receiver's email server will reject it due to attachment size (some do), I upload the file to Dropbox and use the built-in public link tool to simply send a link to the recipient, where they can download the file at their convenience.  This has also been nice when I want to share photos with people after an event.  I just zip them up and blast the link to everyone via email, so they can import the pictures into their own photo management tool of choice.
4. Synchronizing Passwords. On my Mac, many of my passwords for various programs (including Safari) are set within my keychain file.  I have moved my keychains file into my Dropbox folder and created a symbolic link back to where it should be.  Now the keychain passwords work as usual, but are synced between my home and work Macs.
5. Collaborating with Others.  When working with another designer or developer, it helps to have access to the same files, so we can share a folder just between us via Dropbox.  This also is useful between family members, as I can just drop a file into the folder that I share with my wife.
6. Instant Mobile Viewing. There is a lot a mobile device can do, and storing a massive amount of files is not one of them.  I can store all of my documents within Dropbox, and whenever I need to view them on the go, I can use the Dropbox App to download them only when I need to view them.

One of the most powerful methods of using Dropbox is by syncing a particular folder, and creating a symbolic link in the original location.  Through this hack I am able to sync the settings of almost any app on my Mac.

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