One of the biggest strengths of Theora was the ability to easily re-encode video on the command line with the tool ffmpeg2theora. Theora encoding could be accomplished by passing flags to ffmpeg, but the ffmpeg2theora handled common settings and detection and made converting existing files even easier.
For me, one of the biggest successes for WebM will be when a command becomes available, and is released in the package systems that allows users to simply run ffmpeg2webm when encoding. I'll be re-releasing my videos as a WebM gallery as soon as Firefox and Chromium stable builds have WebM support, or sooner.
Desired man page
Take the following man page as an example of what I'm hoping for.