According to this review, (http://www.engadget.com/2012/05/29/samsung-chromebox-series-3-review/), extended desktop will be a feature added later.
"The OS also handles display mirroring and swapping, with spanning to be introduced in the future."
amazon instant video works on the chrome box. I haven't noticed any chopiness, the video is clear. There was an update to chrome that made it so amazon instant video didn't work for about a week though, but other than that, it's been working well.