Priv.ly is an open source project that allows you to communicate with others using the site of your choice while denying that site access to your data, everything is encrypted and shared through a link, the site can not be forced to reveal data it doesn’t hold and data retention won’t matter, by posting your messages through a link Google+, Twitter or Facebook will never have access to your private data. The messages will be automatically decrypted by people using the Privly browser addon making the process easy an automatic for everyone, only users whose public encryption key has been used to encrypt data will be able to read the message, it is possible to revoke access to a single user by not using his key and the content on the server can quickly be destroyed or changed.
At the moment Privly servers host the encryption keys to automate decryption and the extension pulls the encryption key and content off the server after your friend clicks on a Privly URL link, this makes the central server vulnerable to attack, there are future plans to change it by creating a P2P decentralized storage system making impossible even for Privly staff to read your messages, another vulnerability that the developers are working on is preventing the browser from caching encrypted messages.
Privly is an asymmetric public/private encryption key system, you could do this yourself encrypting your messages with PGP/GPG before posting them to a social network, Privly advantage over manual encryption is that it saves people time and makes the process easy by only needing a browser addon, their central delivery server also makes it possible to change or destroy a message after posting. You could try to achieve the same result using a self destructing messaging system but few of those services, if any, is open source. Privly is a good initiative to stop abusive social networks data retention policies and to stop censorship from software scanning the Internet for keywords.
The key for Privly to work is adopting a standard that everyone will understand as soon as they see it, in this case a URL, having too many ways of doing the same thing does not help spreading a technology, it all comes down to everyone agreeing on a system. You still have to solve the anonymity side of your messages as your computer IP is visible when you post a Privly link to a website.
Note: The project is still in development and might not be stable.