FROM THE DARKCOIN FAQ:
What is the difference between Zerocoin and Darkcoin?
The first obvious difference is that Zerocoin doesn't exist yet.
In theory Zerocoin offers superior anonymity compared to Darkcoin's DarkSend using advanced, yet untested, mathematics.
The main problem of Zerocoin's implementation is that the whole network is encrypted with a single key that is generated during the birth of the network. The party responsible for creating the network key must also be trusted that he has destroyed the key without knowing it himself. This creates a trust dependency in Zerocoin's implementation that is too large. Has the initial key been destroyed? Does someone have it so that they can see every transaction transparently? Will the key break some day and allow every transaction to be seen in plain-text?
Darkcoin uses simpler solutions that do not require trust. Coin mixing is a simple and tested solution and that will be enhanced in the next iteration (Version 2) with ring signatures and IP obfuscation for maximum, yet trust-less, anonymity.
Please read it: http://wiki.darkcoin.eu/wiki/FAQYeah, that's about the depth of my undertstanding. Zerocoin has been in development for a lonnnnnnng time, correct? Is this info in the wiki the latest version? I know they had issues with sizes on these keys you need to download for a transaction (something like a gig per transaction??)
I have no idea what happens next, it's like the good old BETA vs. VHS WAR!