For some of my websites, I've even gotten $0 per click! I don't get it either.. I mean, when I try using adwords myself, there's no way I'd be able to get a deal that good!
It depends upon your niche. Sports , celebrity websites dontearn as much as forex, currency related sites.
But the popular celebrity, games, ringtone, myspace type ad's are the ones that get clicked most often - in my case anyway - where as health and credit (the high paying neiches) are harder to attract clicks to. I guess it comes down to your audience and surfers, I found the neiche that works for me and my visitors, I am no longer focused on CPC - I focus on CTR and boosting traffic.