As an end user myself on Linux, I was worried to read this. I keep teaching materials in the Dropbox folder so only a small file size, but they are important. As mentioned below at http://news.ycombinator.com/item?id=4704176 I have developed the bad habit of editing files directly in Dropbox. I may need to revisit this and use Dropbox as a sync only, edit elsewhere and copy over.
The command
find /home/keith/Dropbox -size 0
shows only cache files for deleted files, and some backup files that I saved while empty (I know those should be zero bytes).
A personal work around is a simple bash script to copy Dropbox directory to another with the date as directory name, I'm running this once a day or so. Then my normal old-school backup onto an external drive will catch each day's dropbox.
Surprising how convenient I found automatic file sync, and how quickly I came to trust the dropbox daemon running in the background on 3 computers!
The trust my mother had in dropbox is now gone, and probably will remain so for the next couple years.