There is a British Conspiracy guy who did a show on google, and in that documentary google official comment was that all user data, toolbar queries, searches, times, dates, frequency ETC, was stored for an indefinite amount of time, or until they felt they had a threshold of such data. (which hasnt been reached yet).
BUT, you can also find representatives that give answers like this, saying that its deleted forever.
http://www.google.com/support/forum/...00891fbc&hl=en
Bottom line, once adsense began being run in gmail sidebars it became 'useful user data' that directly effects their bottom line, and that of their advertisers, so I guess, do the math
