Google moved the content network placement feature into the mainstream today by adding a new tab to the standard AdWords interface.
The content network has had considerable attention from Google over the last year or so in an effort to make it more accessible, flexible and transparent for advertisers using it and the unveiling of this new tab represents their confidence in the new improved network, well that and the earnings potential it has for them!

Once you log in you can take a look at the placement tab by navigating to an adgroup, you can then click it and find relevant sites running AdSense to place your ads on, it’s just a case of locating the sites by one of three routes.
1) you can browse categories to locate relevant sites
2) you can search by keyword(s) for sites
3) you can search by URL(s) for sites
Once you have a list of potential sites to choose from you can then check out the sites by visiting them to ensure they are of a quality that you deem suitable for your site/brand/product/service to feature on and the traffic levels are worthwhile, you would then add the sites you wish to have your ads appear on and then set the cost per click you are willing to pay.
Once everything is set and you have your ads showing on specific, relevant sites on the content network up you still need to monitor the traffic that is sent, Google have made a real effort to increase the quality of the content network but still there are some publishers out there who’s traffic isn’t the best or even human in some cases so when using the content network placement feature you still need monitor traffic very closely.