Ideas like darkcoin are quite interesting, but i think overall since darkcoin does not have a fully open-source code, there is a fundamental problem there. Is it even a bitcoin?
Darkcoin uses similar tech to dark wallet. In addition it needs some "supernodes"? which can be a target for NSA type of surveillance. Isnt that similar to tor nodes that many are currently owned by gov agencies? I like darkwallet more because it is peer to peer...
As DAT other methods might boost the anonymity further.. I read that zerocoin type of tech does not need a bitcoin change just someone to implement it. Dont understand how though.
Blockexplorer is just a website and gets information from bitcoin network which is public so the approach of second key will not fly.