Perian is even recommended by Google on their WebM page when you start looking for a way to get WebM content on Mac OS X.

Let's be clear: we're not killing Perian, we're just done actively developing it. For my part, I'll work to keep it functional as it breaks on versions of OS X I use, but I'm lagging by a full major version these days because I really only need OS X for the unix layer, and Apple isn't moving the platform in a direction that makes life easy for things like Perian (which we'll never be able to meaningfully codesign as an app, for example).