I have no problem playing Youtube clips inside MicroB at fullscreen on my n900. I have the zoutube app installed but it keeps crashing/not responding when attempting to play videos.

I thought the 9 trailer was HD but I stand corrected. The quality is pretty decent though. My desktop PC can play full HD clips with no problem, in fact, I haven't used a modern desktop PC (5 years old and younger) that couldn't play HD smoothly.