Storage in the Cloud does not magically remove the need for security, and especially that rare creature, the security audit. From a post over at labnol, we learned how to do a Dropbox security audit, which is important for obvious reasons. However, this requires vigilance and a repeated review, something scheduled in your calendar. For example, I've just run these tests and had to remove access from a computer which I no longer own. The steps below improve the audit at labnol, and correct a URL change as well.
Audit - Step 1 - App Access
Check the applications enabled to access Dropbox. Anything suspicious?
Audit - Step 2 - Account Access
Check the accounts enabled to access Dropbox. Anything suspicious?
Audit - Step 3 - Event Log
Check the events log on Dropbox. Anything suspicious?
Audit - Step 4 - Sharing Access
Check the sharing access on Dropbox. Anything suspicious?
Audit - Step 5 - Storage Available
While you are at it, check storage available on Dropbox. After all, availability is one aspect of security.