Zerocoin is NOT an alternative currency. It is a proposed extension to Bitcoin to solve the lack of anonymity in Bitcoin transactions. Since all transactions of every Satoshi ever spent is recorded in the blockchain, you can imagine how easy it is to map out the connections, deduce owners, and see who has how much, and where it went. It is like a built in mixing service.
The Zerocoin name is unfortunate, as everyone seems to *assume* it must be some derivative cryptocurrency, when in fact it is an anonymity extension to Bitcoin.
My bad. I was just throwing names out there which I knew nothing about.