Any hardcore developer must be dying to work at Google, Twitter, or Facebook, right? Well, no; see this post by Dave Copeland, “Why I’d never work for Google, Twitter, or Facebook”.
I generally agree with his points; if your core business (where the money comes from) is advertising, your customers are the businesses who pay for the ads, and — to put it bluntly — your users are your product. However sophisticated the services you offer to keep your users around (viewing ads…), your relationship with your user/product is unavoidably marred by this fact. “I’m giving you things, on the assumption that I can convince you to give sufficient money to my actual customers.”
As a developer, I’m not interested in pushing ads any more than Dave is (though the point is academic, since I’m not exactly being recruited by the “big three” — but the principle certainly influenced my job search last year).
It’s not just that I’m not interested in advertising, though. Any company’s actions in the world have myriad effects on lots of people, from tiny to grand scale, and delivering better and more effective advertising is a net negative.