Update: I asked Paul Buchheit for some clarifications on the issue, as some of us were getting interested in the development time line of Gmail and AdSense. Paul tells me that he started working on Gmail in late 2001, though it was just him in the beginning and he was still wrapping up his work on Google Groups. Later that year, Sanjeev Singh and Jing Lim were added to the team. Paul says he then added content targeting ads to the prototype around the first half of 2002 (Paul isn’t precisely sure about the month, but says it might have been March or April).

At the time, there were “probably about 100” users to Gmail within Google, Paul clarifies. What’s interesting is that Paul says content targeting had been previously discussed and “dismissed as unworkable”.

Also, as Paul says, he actually did not use any semantic analyzer library found on the web, as opposed to what Marissa stated in the interview. “[I]t was all my code,” Paul writes. After his prototype, a team was assembled, which Paul recalls was led by Shiva Shivakumar on engineering and Susan as PM (I suppose that’s Susan Wojcicki, Paul didn’t mention her last name), though Paul is not exactly sure anymore on this. Paul says, “The content targeting (’adsense’) team moved remarkably fast – although the product wasn’t officially announced until 2003, I believe that they actually had it running on a number of sites in the later half of 2002.”

On another note, Marissa’s version also adds an interesting detail to the time line of the Gmail privacy issue. According to David Vise in his book The Google Story (page 154):

It made sense to Larry and Sergey to profit from Gmail by putting the same type of small ads on the right-hand side of Gmails that Google put on the right-hand side of search results. (...)

Looking at the world through Google-colored lenses, this seemed like a superb idea in every respect. It didn’t occur to Larry, Sergey, or any of the other engineers in senior roles at Google that serious people they respected would strenuously object to the privacy implications of having Google’s computers reading emails and then placing ads in them based on the content of those messages. In their virtual reality, they remained oblivious to the political reality that awaited them.

Marissa’s statement in the interview seem to oppose this: not only did Marissa, no less but Gmail product manager, realize there may be privacy issues with content targeting... but she almost killed the ads in Gmail because of those issues, which she thought of as “creepy and weird” at the time.

Other statements made in The Google Story are conflicting with Marissa’s, and Paul’s versions. Says Wayne Rosing, then Google’s vice president of engineer, on page 155: “Gmail grew out of experiments that were done that involved our ad targeting.” So according to Wayne, Gmail was a spin-off from AdSense, and not AdSense a spin-off from Gmail, as Marissa and Paul say. Perhaps Wayne got it wrong by looking at the official release time line only – Paul and Marissa were certainly closer to the Gmail project.