Let me explain

DoubleClick.net is the main advertiser ...
I think they do about 40 % of all internet ads

That is pretty much so ... yeah, the story is:
It is pretty likely that you will hit a doubleclick ad site while browsing around, remember 40 % ..

So with the cookie they are able to check which sites you browse. At least they can make a little guide for every user

User a visits site b and c and after that site d

They make a little profile for you, what are users a interessts ?
Yeah, they can find out, they know what sites you are visiting .. at least 40 % of them

And now, the next time you visit a doubleclick net ad driven site, you will get targeted ads ...
so, if you browse CDR sites the whole day, once all the doubleclick banners will consist cdr ads, CDRs, software, burners, bla bla bla
I hope I told the story in a easy way

First doubleclick started with language dependent ads, which was pretty nice, but REAL targeted ads, as they do now ..
That sucks
