As of April 15, 2010, all versions of the Opera browser can no longer view YouTube videos. An error message asks you to update your Adobe Flash Player, but after doing this the error message remains.
Hopefully the YouTube tech department will look into this, as I won't be giving up on Opera, especially version 10.51, which in my humble opinion is the best browser I have ever used hands down.
Mods, please forgive me if I posted this thread in the wrong section.