Google Adsense

I have noticed that there are a lot of questions about Adsense around, and although I have mentioned Adsense before, I note that I haven't really talked about it in length.
Adsense is a Google product for placing adverts on a website. If you are looking for an additional stream of income for your website, you may want to consider what Adsense has to offer.
Adsense matches your site content to the large database of adverts that it has. Keywords in the content will trigger specific adverts. If you want to see this in action, you can see how the content of my site: http://www.cassette2cd.co.uk is refelected in the adverts that appear. My site is all about converting old style audio cassettes into CD's, the adverts offer hardware and software for this very purpose. If you visit the 'studio focus' pages: http://www.cassette2cd.co.uk/studio you will notice that the adverts are now aimed towards microphones.
If you are worried about a competitors advert appearing on your site, you can exclude their specific URL using the 'filter' section.
It is impossible to predict earnings using Adsense because of the variable nature of the cost of adverts. Google offers adverts to customers without a specific charge, allowing the advertiser to control an advertising 'budget'. The rate of pay per click could be anything from one cent to several dollars. The trick is to get high-paying advertisers on to your site (I don't know HOW you do it...but this will be your aim).
You can choose how the adverts will look on your page, and you can combine different types of advertising, though there are limits to how much you can put on a single page. You get to choose colours and whether the ads run vertical, horizontal or as a list of links. (note that the list of links only pays when a click is made on the SUBSEQUENT list of adverts).
I can only talk about earnings in relation to my own experience, I currently get (according to Google) about 160 page impressions a day, leading to approx 7 or 8 advert clicks, yielding approx $1 per day... not a fortune admittedly, but pays towards the running of the site.
To make any real money you will have to have lots of page impressions and have adverts that your visitors are going to click on. Ideally you want to attract high-paying adverts to your website, but I have no insight of how this can be achieved.
Now, it is important tp point out that Adsense does not pay out until you reach $100, which to be fair could take some time....at the rate of $1 a day, this is going to take more than three months.
In order to use Adsense you will need to register with Google, which is in itself, not a bad idea as you can access all sorts of other tools for your website.