This is a scary thread. I had a Rev A, and sold it just a week ago - because I had a buyer and I wanted a new one just to have the latest and greatest. Admittedly, I never really watched many videos on the Rev A, but those I did always seemed to play fine... Youtube and such.
I just got a new Rev B and have been reading a lot about video issues. I have found some interesting things... if it is flash based, it runs like crap... stuttering and stuff right of the bat. Also, the processors run at 60% and heat the MBA up to 80C (seen thru iStat Menus)
Hulu seems to be fine, YouTube seems OK, but I tried watching a long (60 minute) video and I could only go about 5 minutes before it got choppy... I think that was flash based. If I stopped and started it, it would be OK for very short periods.
Meanwhile, on my PC, these same videos use only about 3% CPU insead of 60%. Also, Parallels with Windows XP image runs it better. I am beginning to believe the issues are more OSX related then MBA.
Anyway, after all this rambling, I'm not sure if there is a good answer to the video issues.
I will try watching a long HD hulu show tonight and see how it goes.