I have no issue playing flash content that's outside of youtube. All of my pron and Daily Motion vids load super quick, only YouTube gives me issues... always has.
I opted out of the HTML5 beta shit, and I still have issues from time to time, even on low quality vids that are under 4 minutes long. Yet I can stream full length 720p content from other sources with the greatest of ease.
I never really have issues with YouTube ever. During the Olympics I can stream 720p through their YouTube native player smooth as hell on a single core laptop.