Does advertisements on a website make a website look less appealing?

It depends on the website and the ads.  Plenty of women in the craft space sell a good bit of advertising and it usually matches the look and feel of the site and there's a reasonable expectation that the people visiting the site may want the products or services advertised. Washboard abs, lose fat now, save money on your insurance, flashing gifs, or lots of "underline" in-text ads?  Yup.  They'll drive me away. Philo Hagan supports himself, I believe, from the ads on http://www.hooping.org .  I visit many of those advertisers because they are relevant to my hooping activity. It's all in the context.

More or less, yes. Clean website without any ads will always win against the same with ads. But it's possible to minimize their negative impact so that it would be very little.