I'm excited by HTML5's video tag as are plenty of other people. Once that comes about and once media fragments are adopted, linking to or embedding a portion of a video will be as easy as using the correct fragment on your URL thanks to the Media Fragments WG who has been hard at work since the last time I looked at fragments.
However, until that work is embraced by browsers, embedding portions of videos will continue to require work specific to the site from which you are embedding the video. On the YouTube blog they wrote about how to "link to the best parts in your videos", using a fragment syntax like '#t=1m15s' to start playback of the associated video at 1 minute and 15 seconds. Of course if you want to embed part of a Hulu video it will be different. Although I haven't found an authoritative source describing the URL syntax to use, you can follow Hulu's video guide on linking to part of a video and note how the URL changes as you adjust the slider on the time-line. It looks like their syntax for linking to a Hulu page is to add '?c=[start time in seconds](:[end time in seconds])' with the colon and end time optional in order to link to a portion of a video. And the syntax for embedding appears to be "http://www.hulu.com/embed/.../[start time in seconds](/[end time in seconds])" again with the end time optional.
For more sites, check out the Media Fragments WG's list of existing applications' proprietary fragmenting schemes.
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