Jason Kottke wrote a post on this a little while ago, and I mentioned it briefly in my post about hosted services:  Streaming video has made leaps and bounds in the past several months/year.  In the past, people used to email 3MB videos to each other and forward them to all their family and friends (thanks for clogging my mailbox, idiots).  Then a bunch of sites popped up that hosted these videos and streamed them "for free", accompanied by droves of untargeted ads and popups. 

But recently, sites like Youtube, Google Video, and other "Flickrs of video" have popped up, streaming videos for free with a flash-based player.  This eliminates the need for plugins, codecs, compatibility (for the most part), and downloading.  Everything happens in the browser; there's no need for third-party components (except a flash plugin, which is almost standard these days).