ok I love it BUT I've noticed 2 problems:
1) links must be
http://www.youtube.com ...
http://youtube.com doesn't work
2) Links must be posted with "Reply" - won't work with quick-reply
Not sure how much of a pain it is to add www to the pregmatch but number 2 should be easily solved by adding another plugin with using one of the quickreply hooks.
Still a fantastic product though!