p.s. HTML5 != video without flash. Both HTML5 and Flash have diverse feature sets, a lot of which don't overlap. Even if overnight Youtube and every other video site on the planet switched to <video> using WebM, Flash would still be around for things like games and full flash websites.
Also, as right of right now NO Browser has 100% HTML5 support because it's currently impossible to do so. The spec is a work in progress and isn't finalized yet.