Yes, ads can be distracting. I try not to pay much attention to them and just focus on the site, but sometimes that's easier said than done!
I think the worst ones I've seen (elsewhere) online are the ones that block what you're trying to read, either the huge ones (you have no interest in), or those little "One question surveys," which I would never complete, short or not. Um...if I wanted to do a survey, I'd likely just go to a survey site, right??