According to a statement from the VP of Hulu, they will not be switching to HTML 5 anytime soon.
He did however say they will continue to monitor the development of the new markup language in hopes that one day they can offer a plugin that is universally acceptable to all.
"Not all video sites have these needs, but for our business these are all important and often contractual requirements,"
He also mentioned their new custom Flash player, that will adapt to your bandwidth for smooth jitter free streaming and can also normalize the audio for ads.