I think they'd obviously be great for the entertainment niche websites. But, if you put them on a website in the, say, Internet for Deaf People niche, you probably won't get very far.
Good for video sites, etc. But if you plan on using them make a new youtube account with your sites name as the username. I had the pleasure of linking my account and once the two accounts are linked theres no going backk. I have a General Hospital related site with a RED SOX related youtube name. Sigh.