Federico, thanks for the note and good idea on reaching out to the Toolserver folks to help us track this.
As for the WebM and pros, from my understanding YouTube is transcoding all videos that are uploaded into WebM format. However, I'd be very surprised if even 2% of YouTube uploaders are using WebM as the format. Most likely they are MP4, AVCHD, MOV, or even raw MTS files.
So perhaps it's more accurate to say WebM not used by video pros in their workflow. I'll clarify in the document now.
In the meantime, check out some of the videos produced from our Feb/March pilot with Alverno College.
-Andrew