There are some very cool things you can do with Dropbox and many sites around the Internet will clue you in (See the REFERENCES below). I'll concentrate on some things that are more Linux focused.
I'm a big fan of the Zim Desktop Wiki in that it helps me keep notes about specific configuration issues, tips, tricks and other useful info. But as designed, it is limited to a single desktop machine. I have several that I use, a few in remote locations. The solution? Zim keeps it's info in ~/Notes. Simply move the Notes directory into the ~/Dropbox directory and then symlink it back to ~. Now create the same symlink on every machine you use. Dropbox has now synced you Zim data to all your computers.
There are also a number of suggestions that you can do the same trick with ~/.mozilla. The only drawback I see is that you don't want to waste Dropbox space for the Cache files. Just keep the cache local by using about:config to change the value of browser.cache.disk.parent_directory to /tmp . Then you don't waste bandwidth or Dropbox storage on them.
You can only run one instance of Dropbox per user, but you may have multiple users on your system, each running their own personal instance with their own 2GB storage. Send each user an invitation so you get more free storage and let them set up their own dropbox accounts. Start the Dropbox daemon from rc.local like this:
su -user1 -c /home/user1/.dropbox-dist/dropboxd
su -user2 -c /home/user2/.dropbox-dist/dropboxdetc.
While Windows users have problems trying to run Dropbox like this as a "service" such as needed for Mac and Windows users to stop the service to access the individual Dropbox management GUI, Linux has no such problems. When the user logs in, they will have a Dropbox icon in their tray and their files will be freshly synced.
While the tip to install portable Windows applications is nice, Linux users can keep shell scripts, custom config files, self-compiled software packages and so on for use anywhere.
Get the Linux Dropbox Application
$ cd ~ && wget -O - "https://www.dropbox.com/download?plat=lnx.x86" | tar xzf -
$ cd ~ && wget -O - "https://www.dropbox.com/download?plat=lnx.x86_64" | tar xzf -
Get the command-line script:
$ wget https://www.dropbox.com/download/dropbox.py
Put it in ~/bin and chmod +x it. Use --help to see its options.
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My initial space on DropBox appears to have been a special Sprint promotion and, unless I elected to pay for the additional space (I had filled it up), my account would be frozen. I elected to set up a private ownCloud server. I still use DropBox for my business account.