I haven't been able to play back a video in the cloud so far. I'm not sure if I just use a wrong codec or if it isn't supported at the moment.
As I work as freelance filmmaker this is really essential especially when working with a client. If they can't view it in the browser I have to zip the file upload it and they have to download it which isn't the best solution. With dropbox and skydrive I have the option to view quiet some video formats right inside of the browser.
Please add this feature it would be big bummer if that wouldn't work. You doesn't have to support all the formats the Media Encoder can export. Just a few options would be great (and make sure to include presets into the Media Encoder)