I support this. Because when I first wanted to post a youtube video on the forums, I had to quote around other people's post with youtube videos and that was a hassle. But I grew out from my noobish ways and know that tag at the back of my hands.
Definitally support this.
It would also be nice to explicitely state what part of the URL needs to be used. Videos tend to not work for me when the "v=" is included, only the combination of letters and numbers allows for playing.