I am sure YouTube has some pretty capable UI designers - they certanily can afford them. Unfortunately it looks that moronic managers have a bigger saying:"Screw usability, make it look COOL!"
Another idiotic decision was the addition of on-screen comments and having this turned on by default. "Look here, lol" or "Click here to subscribe to my crappy channel" (a sure way not to get a subscribtion) It annoys me every time I forget to turn it off. If you cannot express your intentions through the vid, well time to work it over.
I see Dowly's point regarding ads as a support for people who are worth it. I don't agree with the decision to show them at the start of every video. This way it creates revenue for the user even when after 10 seconds in the vid someone decides it's not worth watching. A better way would be, having it the TV way, after a certain time in the vid - or the folks could just create a good old website, where users who decide to support them can decide to click on ads.
So I don't feel bad having disabled ads and also the comment section - it's so refreshing to solely watch a vid without (unintentionally) reading idiotic brainfarts.
Finally a tip for everybody who knows that ESC disables fullscreen after having read this for the 1000th time. There's a little program called "Flash Fullscreen Patcher" which disables this annoying overlay which destroys the video flow to me. This has been a decision made by Flash, not YT, but anyways it's still very helpfull in having a better viewing eperience.