I didn't mind little banner ads here and there when they weren't being intrusive and were politely embedded in the rest of the page without being disruptive.

But wow, you turn the adblocker off and the swarm is almost immediate. From what I've heard, Youtube has become a cesspool of ads going off constantly. Songs getting disrupted right in the middle to play ads and getting more ad time than actual video time are just a few of the problems I've heard.