I recently wanted to send someone a clip from The 'Burbs on YouTube, but I wanted them to see a specific line from the movie. I knew that if you added a timecode in MM:SS format to a comment that YouTube would parse that as a link to that timecode in the video, but I figured they had to have a way to do it in the URL as well.
After a little bit of Googling, I ran across this post from the New York Times, that explained exactly how to do it. I hadn't run across this before, so I thought I'd share to perpetuate the knowledge.
If your video link is http://www.youtube.com/watch?v=krsdKDkyQds and you want it to jump to 5:40 in the clip, simply add #t=5m40s to the URL: http://www.youtube.com/watch?v=krsdKDkyQds#t=5m40s
This doesn't seem to work for embedding, at least not with the WP plugins that I'm using or by hacking it into the embed code from YouTube. If someone knows a work-around for this, please post it in the comments. In the mean time, if you want to enjoy the specific scene that I wanted to reference, you'll have to drag the playhead to 5:40 manually. The clip ends at about 6:50. [Edit 4/9/2013: The video clip referenced no longer exists.]