Kywser basically you need traffic, lets do a simple calculation, you have 10,000 unique visitors to your site each day and you have an avg CTR of 2%, this means 200 of these people have clicked on your adsense ad, your avg cost per click is £0.20, you have made £40 for that one day, £1200 for the month. Thats simply how you can make money from adsense
Thats totally not true, of course there are other ways to make money with traffic, but by placing a simple ad you will earn more, I rather person leave my site from a related ad pinpointed to them than any other way, wait til that simple ad is making you £100 a day extra on top of all the other methods you use to make money, and you will find that adsense is very very good, with very little maitenace at all.
If no one does why would you see Adsense ads everywhere? Read POF's story http://www.google.com/search?client=safari&rls=en&q=plenty+of+fish+adsense&ie=UTF-8&oe=UTF-8
I look at it like this: if there are people that want to drop Adsense because they don't think it's fitting, then that's them. I say more ads for the rest of us.