The real hacker is most likely DudeTubeHacker, he made an attack list long time ago, and followed it as planned.
Someone also made the youtube account "saadzim", trying to take adventage of the situation, and pretend to be the hacker, commenting "haha I hacked you" in various videos (Some people will probably ask him how he has done that, and he'll answer them that if they will give him their passwords they will know...)
No accounts were hacked, only the titles. About 2K video titles were hacked, probably the hacker abused a bug in the HTML script, I have no real idea, maybe you do.
Maybe this hacking operation will get him a job in a High Tech company, who knows.
It took youtube 3 hours to take control of the situation. The next attack will probably come soon..
Sorry for digging I am just bored.