As with most folks here I was struck by the wholesale adoption of the 'brilliance applied to clicks' meme. For those who aren't aware of it, its the 'pay the best and the brightest minds to figure out ways to get me to click on ads.'
It makes for a great sound bite, but it is completely and utterly wrong. To a first approximation, these internet services don't write ad copy or design ad banners, and that is where all the effort goes into figuring out how to get you to click. So don't work for an ad agency :-).
Now what the folks at Google do (I have no direct experience working at either Facebook or Twitter) is make it so that the system they have can reliably and efficiently serve advertisements into designated spots on the pages. This problem is a combination of bin packing and economic theory and systems design. Trust me when I say that the engineers working in ads (and they are a small fraction of the company) probably don't care at all whether or not you 'click' they care that they can see the query/page, do the auction, and provide an ordered set of results in under a few hundred milleseconds. But lets talk about clicking for a moment.
Ads are a 'tax'. They are a way to subsidize something so that it costs the consumers less. They do that by selling access to the consumer's eyeballs. Taxes, like prices, influence consumer behavior (just ask any town in California (8.75% sales tax) borders Oregon (0% sales tax)). So the upper limit on ads (as a tax) is when they start driving consumers away.
Like many people I find that some advertising levels are intolerable. I used to regularly read some gaming web sites until the tax of dealing with all the advertising became too high. (even with Adblock for web sites, or arriving at the theatre 10 - 15 minutes post start time so that you can just see the movie, avoiding ads has a cost too). I wrote a local radio station and explained to them that a particular ad they played caused me literally to change the station when they played it, generally leaving me on their competitor's station. You can't tax your way into a successful business model, and if you can't afford to offer the service with a combination of upfront cost and tax then you just quit while you are ahead.
The original post reminded me of John Cuzack's line in "Say Anything" - 'I don't want to sell anything, buy anything, or process anything as a career. I don't want to sell anything bought or processed, or buy anything sold or processed, or process anything sold, bought, or processed, or repair anything sold, bought, or processed. You know, as a career, I don't want to do that.'