doubleclick.net is an advertising host.
You see their ad's on thousands of sites across the net.
They track clicks on their banners before directing you to the site that they are advertising, using the track logs as a method for charging the advertisers.
Examples can be seen at
this online tech newspaper, for example in the story about
Fasthosts (hover your mouse over the banner ads above and to the right, and you'll see that they are doubleclick ads - check the status bar on your browser)
Not neccesarily bad, and it does make it easier for those who don't want the ads to block them - one simply has to block the urls via a host file, or firewall rule. (or browser plugin)
Nothing to do with PN at all.
