I love Dropbox and have written about it several times. See http://goo.gl/rnZVf for my past articles about this excellent online backup and file copying program for Macintosh and Windows. I know from comments posted here that a lot of newsletter readers are also using Dropbox.
One of the "downsides" of Dropbox is that its default operation is to only backup and copy files that are in the Dropbox folder and any subfolders under Dropbox. The default operation does not back up \My Documents or \Documents or other folders.
I solved the "problem" by not using the Documents folder. I simply moved everything from /Documents (or \My Documents on some versions of Windows) to the new Dropbox folder. The Dropbox program then backs up everything under the Dropbox folder. However, not everyone wants to move their files. Some computer users prefer to keep their files under \My Documents or under \Documents. In addition, a few programs do not store their files in either \My Documents or in \Dropbox. Luckily, there is an easy method of making Dropbox back up ANY files.
You can tell Dropbox to back up any files by the use of Symlinks. That sounds complicated, but an article by Jeffry Thurana in the Make Use Of blog explains the procedure step-by-step. Even better, the article includes screenshots from both Macintosh and Windows systems, showing how to make Dropbox back up ANY files on your computer.
You can read Jeffry Thurana's "How To Easily Synchronize Folders Outside Dropbox Using Symlinks" article at http://www.makeuseof.com/tag/easily-synchronize-folders-dropbox-symlinks/