All MIX11 sessions are availalbe to watch, stream or download at the Channel 9 events section. You can smooth stream sessions, download video in WMV or MP4, get audio-only versions, and download extra files like powerpoint decks. There are a couple other ways to consume the media ranging from point and click down to getting your hands into code and scripts:
I'm sure there are plenty of ones I've missed, please feel free to post additional options in the comments. We're also always looking for ways to streamline the online conference experience so please give us feedback! This year we've moved media from every MIX to a single video vault on Channel 9. Past PDC videos are also available and they're all linked to speakers that have held sessions across multiple conferences and years.
Some details and rough device guidelines
*iPhone doesn't support WMV, so you're probably best off grabbing the MP4 High version