From Mark Pilgram:
…the DMCA requires an ISP to remove the offending content immediately, as soon as they receive notice from the alleged copyright holder. Only then does the accused have the chance to refute the charges, after being knocked offline and dragged through your ISP’s bureaucracy. As you might imagine, this is already leading to DMCA spamming from copyright holders, since there’s no downside for them in doing a Google search and sending a letter on every search result. That’s precisely why the DMCA is such a bad law: it’s rife for abuse, and it is being abused, and this is what it looks like when that happens.
Don’t you see here? The DMCA enforces a change in the burden of proof: you’re guilty until proven innocent.