[ekalvi]

I think obfuscation is a factor. However, I think there are two other factors that should be considered: 1) the call to action is much clearer in the MS Paint ad "Play Free", and 2) the polished ad "looks" like an ad, whereas the MS Paint one doesn't, because "who in their right mind would make an ad that looked like this?"

On the second point, if everyone started making MS Paint ads then users over time will get used to the style as well, and stop clicking. People have an internal ad blocker that takes time to "learn" from existing patterns.

We once did an experiment with Google Adsense. Directly above the ad unit, if you used a large, clear heading "Sponsored Ads" and then compared the results with no heading, the clickthru rate differences were very significant. I don't have the exact number, but something like 3-5X in favor of no heading.

To improve CTR, you can either make a very compelling, contextual ad, OR trick your users into not knowing something is an ad. Tricking is easier and more effective in the short run, but will get you in trouble once your advertisers start looking at their conversion rates and ROI.