Just another way Google can track you and gather user information. Like on the same page, they have the unique identifier IDs set to expire in 10 years. So basically they track every search you ever make in google. That and all the other information they gather about you with their search engine and services. Their email, Gmail, Orkut, YouTube, Google Docs, their new services which will index your medical records for hospitals and doctors, blogs, you name it.
I use google myself, so I'm not an anti-google person but lately they have been getting as bad as Microsoft and Apple lately. Their "Do no evil" policy doesn't seem their top concern anymore. A shame, though while its one of the better companies right now, they aren't as good and perfect as many people think. ;p