Oh, that thing?
Where websites suddenly sprout "toolbars" that eat window real estate, obscure the content I came looking for, eat cycles, and then turn out to refuse to turn the darn things off? Because, oh, my browser window isn't full screen all the time and hey my screen is only 1024 pixels wide so any off buttons just happen to lie right outside the window, and without scrollbar are so effectively unreachable? Those "features"?
Or the same thing but that only pops in until after you've scrolled down a bit? Or maybe those things that pop in at the end of an article "go read this too"?
I hate them. All of them. They get blocked any way I can. Along with moving anything that isn't the main focus of the page. Foo, ads that don't move are obnoxious enough. That stuff is so much worse.