I know most of us here are webmasters but I am curious in reasons on people clicking on ads. They may have some reason we never uncovered.
It's kinda like the golden rule, do unto others as you would have them do unto you I click on their ads because I want them to click on my ads
You forgot to add "I don't click on ads." Seriously, I avoid them. I know if I click on an add it's just money wasted for the advertiser (forget about the publisher making money, without the advertiser programs like Adsense wouldn't exist) and I like to save them a little cash and go to the site directly.
The only option for me to click on an ad is your third option. "I found really interesting ads. which encourage me to click on."