This issue came up a little while back. We run a very small percentage of Google ADs on our site (less than 1% of the ad views). Google apparently tracks your interests from site to site and attempts to show you relevant ADs. Don't be mad at Google alone, Microsoft, Yahoo, AOL and every other major company that is in any way associated with advertising is doing it.
Anyhow I ran into this a moment ago Google Ads Preferences
You can see what Google thinks your into and you can opt out as well. Not that it will do much good as the first time you clear your cookies you will have to opt out again. Apparently I am into computers and news. I am also in the 25 to 34 demographic.