Balance out commercialization and quality of content

As user as users are concerned, I presume that it's better to not have any ad on your site.  Some users may see that not having any ad implies better quality of content.  However, you, as a publisher, need to display ads (in most cases) to generate revenue.  How do you balance this out?

You obviously need to run ads to generate revenue.  No doubt about it.  But the question is "How many"?  Also how intrusive should they be?  And this is when I ask "How do you balance out "commercialization and quality of content"?