I don't care. I use Dropbox because of the unparalleled feature set and ease of integration. I have my taxes stored on Dropbox, along with a lot of other sensitive information. They're in an encrypted RAR file with a line-noise passphrase, just like they would be if I were storing them anywhere (including locally -- after all, what if Mallory steals your hard drive? Or, to parrot the most common movie plot threat, what if the NSA secretly breaks into your house when you're out at the movies and images all your disks then slips them back in without your knowledge?)

The features DB offers for sharing, web access, etc. are well worth the tradeoff, and I am ashamed to see the security pedants constantly pillorying Dropbox because it's not some imaginary "verified secure" system. They don't advertise to be that. A claim of "we encrypt your files with RSA" should be utterly meaningless to you without knowledge of how the key is controlled, and a few seconds' thought and examination of the feature set should inform you that yes, Dropbox has to have the key to decrypt the files. That doesn't make the claim of "your files are encrypted" any less true.