I just noticed while browsing O'Reilly's P2P site that all their ad links are redirected through DoubleClick's servers. I have my browser set to refuse most cookies, especially DoubleClick's.
Doubleclick has had run-ins with privacy advocates in the past, especially since they started using "web-bugs" – single-pixel gifs served from Doubleclick's ad servers design to facilitate user tracking through sites.
Frankly, with O'Reilly's involvement with the open-source community, I'm suprised that they're using DoubleClick.
The open-source and privacy-advocacy communities have a lot of overlap, and I could be wrong, but this seems that it could come back to bite O'Reilly.