The current blocking may be related to the Communist Party Congress, which began on 15 October in Beijing and ends on Sunday. Chinese authorities regularly blocks access to websites that it finds objectionable, including those dealing with politically sensitive subjects. YouTube could conceivably carry some information the Chinese authorities think it shouldn't. That's what we have been. Blocked. Great Fire Wall-ed.
Now YouTube is inaccessible for most everyone in China, the current block is actually a bit more restrictive than the other block, since any mention of the string "www.youtube.com" in any URL seems to be blocked.
For example: http://www.google.com/search?q=www.youtube.com (if you are out of China, you should use http://www.google.cn/search?q=www.youtube.com) will not go through, and will get you a "Connection reset" error.
That mean the YouTube are not viewable via normal proxy. Chinese user must use secured transmission (SSL , HTTPS) to visit YouTube, that is not suitable because of the slow and instable connection.
The Chinese authorities also block some great website like FeedBurner, Flickr, WordPress, BlogSpot and Wikipedia.