I'm so old school that I find it hard to believe internet advertising is as effective as the industry would like advertisers to believe. They do not influence my spending whatsoever, and judging by many of the comments here, the VAST majority of us are more interested in getting them off the screen rather than seeing what they're trying to sell us.
Who goes online, especially to a forum, looking and hoping to see a bunch of ads? I can understand that site owners need to monetize to some degree what they've built and pay to maintain, but as has been mentioned, there gets to a point where the user experience is so diminished or the site is just so downright annoying that people will stop coming or only come when absolutely necessary. There's also the possible effect of people resenting the ads so much at a site that overdoes it that they can create some extra resentment toward those particular products or advertisers with people mumbling about how sick and tired they are of seeing that same ad again...and again...and again.