Here's the entry from my bank account showing an EFT transfer from Google Adsense. The first time, it took me three years to reach the $100 payout threshold. This time, only 15 months. Right now, I'm on track to make the next payment in a little less than a year if things stay about the same.
Am I going to get rich from Google Adsense? Not on your life. But, it does pay some of the expenses of sites of mine that I host, and that's a big help.
Where do most of my clicks come from? Actually, not on any of my blogs. Most ad clicks are on my West Michigan recreation site Get Off the Couch. I think that is because it is very specific, and ads can be targeted really well.
If you are going to use AdSense, just be careful to follow the rules. For example, this blog does not show any AdSense ads, because I talk about Pay-to-Click sites here, and that is a definite no-no. People have wondered about Adgitize ads and Entrecard or CMF. But I've been using those right along and they've never balked at them.
I do use Chitika ads along with AdSense, and that seems to be ok. Those are targeted in a different way from AdSense, so apparently they don't see it as a problem.
If you see yourself into blogging or having web sites long term, and have good niche sites, AdSense can be a legitimate way to earn.