It will be my primary computer. I'm watching the 1080 content directly on my computer. Sure, there aren't enough pixels on the 13" MBA to support 1920x1080 but I still watch it anyway.
I know my biggest annoyance would be the drag and unresponsiveness.
Well I'd say it'll be a bit slower every once in a while but not by much. Wait for actual reviews from users to come out.
In terms of 1080 I still don't understand why you need to watch it in that resolution. It takes up more space (especially when a 720 mkv is almost as clear and you can barely tell the difference even on a 40inch LED) and will heat up you laptop a lot more.