Pros
Free Food !!! Great people. It feels like staying in college if you are a bottom employee (foosball tournament, PS3, Wii...). You can learn so much from the company and others because everybody is talented. Very fast moving environment. It is a meritocracy, if you are good, you will be recognized and remunerated. You will work in the most international environment possible with colleagues from all around the globe.
Cons
You will not have any career opportunities within the company. The task for the new graduates are pretty boring on the long term. It is almost impossible to move from an office to another, so don't expect to come back to your country if you are an expatriate. You will only meet graduates from the best schools because Google only hire in some colleges, no real background diversity.