My understanding (though I'm not a lawyer) is that under the DMCA, Megavideo can sue. [edit: like dangrossman says, I don't think they can bring perjury charges, but the DMCA does allow them to sue]
If there wasn't a DMCA takedown request then Google might be liable for content put on the site. My understanding is that they must follow the laws to keep safe harbour. This is why Megaupload was able to dispute the claim the first time.
Some information here: http://targetlaw.com/consequences-of-filing-a-false-dmca-tak...