Those sites are usually blocked for a reason. Like for instance our company doesnt block youtube and no joke it accounts for 25% of our traffic. 10% might be legit the other is people watching kittens doing cute things.
Another thing to keep in mind if you company is blocking those sites and you do manage to proxy to you tube they will see a HUGE spike going to a proxy IP range. Any be like why is Yama273 downloading huge amounts of info from that address. then BOOM busted and fired. \