The only reason Im using Flash on YT is Google insistence on forcing VP8 on my old Core2 laptop (intel GPU means no hardware video accel).
h.264 with mplayer plays perfectly in 1080p
h.264 with flash plays perfectly in 720p
VP8 with HTML5 stutters in 720p, and still drops frames in 640x480
If/when they finally remove Flash option I will be forced to script direct mplayer streaming of mp4 files from YT server bypassing their player altogether.