Just one for the future guys. We had an outstanding idea by othe in the dev group the other night. It's not one we intend to implement for a long time (and maybe never) - it depends how things progress, but this is just posted here so it gets archived.
If I ever release the decrypted message, you'd be able to verify that it existed today (11th February 2014) because the signature on the cyphertext below is mine, and if I released the plaintext in future, you would just be able to encrypt it to my public key and generate matching cyphertext, so you would know that I knew the contents of the message today.
GPG key:
http://pgp.mit.edu/pks/lookup?op=get&search=0xFD948CCC1EAB2FB5-----BEGIN PGP MESSAGE-----
Version: GnuPG v2.0.22 (MingW32)
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RWOfV+tg
=uDKF
-----END PGP MESSAGE-----
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.22 (MingW32)
iQIcBAABAgAGBQJS+n/DAAoJEP2UjMweqy+1mjYP/1rAIgWAjEc4HycUKUvAHtP1
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gaB4mtvgMqK3k4HIb5go
=XbO0
-----END PGP SIGNATURE-----