Hi P3t3rb0nn,
Yahoo has more things to answer for, take their "tracking habits" with there what they euphemistically call "web beacons"(see the F.I.B. blog), which are actually third party webbugs. There are also a lot of bots, that start where others stop (robot.txt).
If you do not specifically opt out, all your tracks lead back to Yahoo on their net and outside. The only good thing is, they are frank about this. What Google does is n't even known, the only comment is their motto "Do no evil", and you have to believe them for their blue eyes".
greets,
polonus