According to this link:
"Every video on YouTube will be transcoded into WebM. They have about 1.2 million videos available today and will be working through their back catalog over time. But they have committed to supporting everything."
If true, the implications seem pretty deep. Personally, I'd be less intimidated by MPEG-LA FUD knowing that YouTube, the world's most popular source of online video, is walking the WebM walk. Add to that the fairly impressive list of supporters mentioned in the WebM announcement, and it would seem to be time to put-up (show your real legal teeth) or shut-up (no more FUD) for the MPEG-LA (and recent FUD'sters like Mr. Jobs).
On the other hand, Dark Shikari (the x264 developer) said this in his analysis: "Though I am not a lawyer, I simply cannot believe that they will be able to get away with this, especially in today’s overly litigious day and age". His comments comprise a rather more elevated class of FUD. Could this be the mother of mistakes (by Google) that will allow MPEG-LA to find themselves a mother-load of riches in such a deep pocketed infringer?
Interesting times ahead!