David and Danny are correct - any unauthorized reposting of copyrighted footage is actionable infringement. DMCA protects YouTube in this instance (for now anyway) but does not protect the poster of the video if the copyright holder were to pursue it.
I am of the opinion that posting footage on mass distribution channels such as YouTube not only diminishes the value of said footage, but is yet another instance of footage being given away to help commercial interests without the photographer seeing any benefit. Any publicity value gained by such exposure is only beneficial to the photographer when only 'snippets' or 'teasers' of the footage are given (similar to a movie preview). If the entire clip, or at least the 'meat' of the footage is shown, there is no incentive for a viewer to seek it out elsewhere (via DVD, TV show, etc), thus its diminished value. Never-before seen footage (or footage played on news networks briefly, then pulled after a few days) has greater inherent value to producers, as there is more of an audience willing to tune in to see it (more of an audience means more advertising revenue, which is what makes the media world go 'round).
YouTube has grown significant enough in modern culture to have the potential to reach a large percentage of conventional television viewers. As such, a video that gets major attention on YouTube may be considered 'played out' by potential buyers. Think about it - how many will tune in to see Tim Samaras' footage when it finally airs on NG? How many would make time to watch if the other recently-gone-viral lightning video was going to be on the show instead?
I think YouTube may be valuable advertising for a chaser as long as you don't give all your goods away on it. Give them just enough so they will want to see more.