You should use SoapBox and get the SoapBox team to look into something like the viddler style tagging and comments system. That way you wouldn't need to split the video's up, just tag the time points and have it as a long video, unless the issue is upload
time and such. Also even better than that when people are watching the video they can comment at the time point so that there is a context to the comment
(OK so I'm a Viddler.com fan!)
Oh, so someone's already done it? I had thought about this before, the ability to jump to a tag for the bits you're interested in, like 'Demo starts here' or 'Talking about feature XXX', etc.