Not many users know, but you can link to a specific point (time) in a YouTube video. Just add this at the end of the url: #t=XmYYs, replacing X and YY with the time you want to link to. If, for instance, you would like to link to minute 1 and 30 seconds of a video, the url would look like this:
http://www.youtube.com/watch?v=b-p8kvoyP4Y#t=1m30s
