They recently added a feature to youtube to let you link to a specific point in a youtube video.

Details:

To create a deep link, append the following to the end of a YouTube video URL: #t=1m15s. This says to link to the time 1:15 - you can replace the numbers before the 'm' and the 's' with anything you like.

As an additional bonus, if you mention a specific time in a video comment, e.g. "haha 1:14 is funny", this will become a hyperlink. Viewers can simply click on the time and the video will automatically jump to the point you are referencing.