You can still post actual YouTube clips in the forum (rather than just a link) by using the "new topic" or "post reply" button and then using the YouTube button just above the textbox.
Just click the YouTube button and it will add "[YouTube]" tags to the post, then just paste the full URL of the YouTube page in between. EG [youtube] http://uk.youtube.com/watch?v=goobledegook[/youtube]
In this case