News.com has the response here.
TechDirt has a good writeup:
The filing from Google is pretty much exactly what you’d expect. It points out that Google is well within the law. When Viacom sends takedowns, Google complies — even if Viacom screws up and demands non-Viacom videos get taken down. Google’s lawyers also point out that Viacom was one of the companies that pushed for the DMCA and had a clear hand in shaping what was in it — noting that it’s a bit ridiculous for the company to now be complaining about the law it wanted put in place.