I've previously watched HD streams on the MBA itself at 360p or 480p and the fan will usually spin up and get warm. Last night when I had it hooked up to the plasma using TB to hdmi in extended mode I tried a 1080p flash video stream. Initially it spun up as expected...then it got louder...and louder. The temps according to iStat spiked to as high as 92C. I know some users here reported spinning up when simply connecting to the TB display let alone running video or worse flash video.