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.
I agree with jjhall.
If you use PIE (Pre Internet Encryption) before you store something online, then you are safe (as long as you use a strong password or you do not lose control of your private key if you use asymmetric* encryption).
If you PIE, they you can store your data safely online. You will just have to remember where you put them.
I take PIE a step further and encrypt data when it leaves my system (e.g., coping to a USB). This way I can safely delete that file without having to shred. For this to work, I will not decrypt the file on the USB.
* Also called public-key cryptography (which is what BitCoin uses by the way
). See
http://en.wikipedia.org/wiki/Public-key_cryptography for details.