Google AdSense tracking in Google Analytics
Google has finally launched something that will help a lot to track the performance of your AdSense campaings. If you already own some websites that uses AdSense to monetize, you will love this new feature because it will allow you to see detailed AdSense revenue by website, which was absolutely not possible with the AdSense-only interface.
What is it ?
It is the ability to link your AdSense account with your Analytics account. By doing this, every impression and every click will be tracked in Analytics.
Where do I go to see the detailed stats ?
When you link your two accounts, you will see a new menu item appear in your Analytics account, just like this one :

You will see 3 different menu items under "AdSense" (in fact 4, but the first is only the summary of the 3 others). These are the 3 different statistics you can get for AdSense.
What will I see in "Top AdSense content" ?
You will get detailed stats (total revenue, clicks, impressions, CTR and eCPM) for every page on your website. This is simply AWESOME. With this feature I discovered that in my dating website, the page that is generating the more revenue is the registration page.
Here's what it looks like :

Like any other Analytics graph you can change the view to "table", "pie chart", "performance chart" and the "comparison chart". You can also sort the table columns and change the time period.
What will I see in "Top AdSense referers" ?
You will see detailed stats (total revenue, clicks, impressions, CTR and eCPM) for each referer. A referer is a domain name on which your ad has been shown and clicked. For example, if 2 people clicks on your ad shown on www.example.com and clicks 2 ads each (40c each), the revenue for the referer www.example.com will be 1,60$.
Let's take a look at this :

With this feature you can easily track where your ads are being shown and which website leads you the most valuable members. As you can see in my stats, my most valuable referer is hotmail.
What will I see in "AdSense trends" ?
You will see what you already see in your AdSense account : revenue by day, just like this :

The only difference is that you will get a little bit more because you can choose exaclty what trend you want to see, by using this menu :

How do I activate it ?
Now that I convinced you to use this awesome feature, let's activate it. First, I assume you already have your AdSense account and your Analytics account and everything is up and running on your different websites.
1. Go to "Analytics settings" on your Analytics account and click on "Edit AdSense linking settings".
2. Check every AdSense website you want to track in your Analytics account.

3. Select the primary website. I suggest you take your biggest revenue generating website (the one that has the more traffic) or the website that is the least editable, because for each other website you will have to open the source code to add something.

4. Open the source code of your other websites and put the little JavaScript code block at the beginning of all pages (it may be a good idea to have a master page on your website where you can globally put the code, instead of opening every page).

It is very important that the tracking code (just like the one below) be placed in the "<head>" tag. If you don't do so, the tracking will simply NOT work. Trust me, I already tried !
<script type="text/javascript"> window.google_analytics_uacct = "UA-123456-1";</script>
Conclusion
Google is and will stay for a while the best advertising company on the net. Just try to find another service that provides you the same tracking functionality.
Do I have to buy things on "AdSense secrets" sites to make money ?

You probably saw a lot of times websites with titles like "Google AdSense secrets revealed" or "Making millions with Google AdSense". Those sites encourage you to buy their books, their video advices and other stuff. All they want to do is make money with you, while you think you're learning something to make more money than them.
First of all, stop thinking AdSense is the way to make millions for everyone. Yes, some people makes millions with this program, like Markus Frind (PlentyOfFish), but don't think because you read books and books you will make millions too ! By doing this you will only help people getting richer and richer selling you something you can get for free.
All you need to know to make some money with Google AdSense is everywhere on the net, and free ! There is only some simple rules to follow to succesfully make some money with this. There's not an absolute formula that works every time. Everything is different from sites to sites, you have to try it yourself.
By experience, if you want to make money with Google AdSense you have to try many different formulas. You have to change the size of your ads, the places where you put them, the colors, etc... Each website is different, so every website needs a different advertising strategie. You can find some good ideas if you Google the web for "AdSense tips", but the best school you can have is to visit websites that uses the Google AdSense program and try to see how they places their ads.
The most important thing you need to remember from this article is that you never have to pay to get good AdSense tips. You can find everything you need for free.