It's too far up the stack and too coarse-grained. If I save a file on my Mac, it is encrypted, but if I transfer it to Dropbox it is decrypted and then transferred.

Right now I solve this by using command line tools or encrypted .sparsebundle images. That sucks.

My thoughts are that we could really do with encryption being the default. If I upload a file via gmail, it should be encrypted with the recipients' public key. If I upload a file to Dropbox, it should be encrypted with my public key. Both should be overridable (e.g. public Dropbox link).

The key itself can be kept secure using hardware tokens for encryption/decryption/signing. The major problem with that seems to be access across multiple devices. Would it be possible to produce a wireless access token with a secure handshake that could be used for all devices?

I have no idea how we'd get there or how we'd convince people to go along with it.