The statement from Dropbox's CTO works for me: "The employees can't access your information." Sure, that's fine.
I'm storing stuff that's relevant to me and would be inconvenient to replace/rescan/etc. If I need to store something that requires absolute security, I can throw things into a password ZiP file or a Truecrypt file. If I have something that I think absolutely no one on Earth should see? I don't store it online, that's for sure.