WhatsApp for Android has implemented Open Whisper Systems end-to-end encryption (not available for iPhone yet).
Is this a win WhatsApp (and Facebook)? It probably won't get me to switch (even as tin-foil hat as I am), because it's still not 100% open source, and cannot be audited. It's not the code or that math that is trustworthy, it's the implementation of the code that is critical here. My hope is, this will further push other messaging systems to help users "go dark".