If dropbox were to offer encryption, it would not make things more secure since I'd have to hand them unencrypted bits.
If I were to store bits that need encryption on a service like this I would encrypt them before I hand them off.
If I were to store bits that need encryption on a service like this I would encrypt them before I hand them off.
The web client is a bit more of a problem, they would just have to promise to encrypt it right away.