Ads should be explicitly opt-in. Not even "implicit" opting-in or opt-out. You should specifically say you want to see ads before seeing them. And if that means no more billboards, ads in bus shelters, ads on radio, etc. then I'm all for it.
Perhaps we need a lot fewer servers? Servers that are useful will probably be fine, such as this one we're talking on, that I'm sure gets enough donations to be fine. Servers that spew unwanted ads, well, no great loss.