Hmmmm, I wouldn't trust dropbox right now: they had a seucirty breach (due to a bug in an update) on Sunday that allowed full access to every account. The only way, in my opinion, to have peace of mind, is to handle all security measures yourself.
Hence the reason I said to put a TrueCrypt container there, even if someone gets it it won't be useful as long as secure passwords are used. Nothing is 100% secure of course, but that should be sufficient for most all cases. If you're really paranoid, use GPG to encrypt the truecrypt volume before uploading it, of course you still have to keep safe backup copies of said GPG key.