As a webmaster I never click on an ad, I know they are ads and can spot them a mile away. It's possible the ads might serve my purpose or give me the info I'm looking for but since I expect a sales pitch I avoid them.
Anyway - non-contextual ads negate the need for unique content. The ads are divorced from it and there's not a darned thing you can do about it. That's my real complaint.
Imagine if serps went non-contextual too. Doesn't matter what you search for you see what Google thinks you are interested in. Looking for lingerie? Too bad, we think you love SEO more so here's some SEO sites. Not good!