What's the functional difference? It's a way of combining assets then removing them such that tracing becomes difficult/impossible. The link I gave warns about hiding transactions over $10k, as I understand it doing that with zerocoin would be illegal.
The wiki page on mixers [0] suggests that doing this with a large amount of money could be seen as structuring [1].
https://en.bitcoin.it/wiki/Mixing_service http://en.wikipedia.org/wiki/Structuring
^ In the US