You don't expect it because it doesn't occur with other OS's, but it's common functionality with web search. I'd prefer that it was off by default, but if the only price I pay for what I find to be an excellent free OS is that I have to toggle ads off, then I'm OK with that. Your opinions about the UI are subjective, of course; I find Ubuntu's search UI to be better than OSX's Spotlight. I also don't find sluggishness to be an issue at all, in fact I experience just the opposite.