At Viddler, we are working on HTML5 feverishly but allow me to do a quick brain dump on personal thoughts on HTML5. It’s guaranteed that this list will change over time.

The Good:
- Lower CPU requirements
- Open standard
- Works great in mobile environments, keeps power usage low

The Bad
- No support for closed captioning
- Javascript based when you want to design the player
- Javascript is a security risk for hosted environments, like Tumblr, Facebook, WordPress.com, RSS Readers
- No Internet Explorer support (coming in IE9)
- Lack of Security on Stream. tags need open access to streams.
- Ad Serving Not Possible, initial implementations include giving out Javascript tags
- Autoplays randomly when loading pages using default tag
- No Room for Interactive Experiences – Overlays/Sharing functionality/

As of today, support HTML5, it’s great in mobile experiences, but it has a long way to go before coming the default in desktop browsers.