Avantages
Brilliant, funny co-workers. Most of the time, if you make it through the hiring process in Mountain View you're a mensch. I cannot overstate how wonderful most of the people are. Insider access to technology that will drop your jaw on a daily basis. The ability, for good or bad, to help change the world. Spectacular bonuses that bring up the low salaries to a nice level. Google is a good place to join if you are brilliant, good at promoting your work to other engineers, and willing to work 70-hour weeks. The food is pretty darn good. The gyms in Mountain View are extraordinary; I don't know about other sites. They don't want you ever to have to step offcampus, and you pretty much don't.
Inconvénients
Severe caste system: be an engineer or be nobody, and there are ranks within engineering. Quarterly semi-secret stack-ranking system; goal of getting rid of the bottom 5% every year. (Sound like Microsoft? Yup.) Bi-annual self- and peer evaluations. In short, the promotion and evaluation process is exhausting, neverending, and notoriously unfair. If you work in a "distributed office" (outside Mountain View) prepare to be seriously out of the loop and to have limited access to the cool projects and the ones that can build your career. The company used to be just as adorable as its publicity. Now it is so big that it can't be. By this point (2010) Sergey and Larry are completely clueless about actual life at the company and the open-questions meetings consist of somebody asking a serious question, Sergey making a joke, and the question dangling unanswered. When you hear someone bring up a serious personnel problem, it's either too confidential to discuss or it couldn't really have happened. The famous "20% project" where you get one day a week to work on projects you dream up yourself is openly admitted by senior executives to mean "work you do on the weekend", not "work you do on Friday". Do NOT depend on the legendary day-care program. Last I heard there was at least a year's waiting list. There used to be a three-year waiting list, but they solved that problem by raising the fees so high that most Googlers couldn't afford it. (Seriously. It was out-and-out explained that the oversubscribed daycare was an economic problem, and higher prices would resolve it.) Come to Google for technological challenge; come for brilliant co-workers. But don't come for a kinder, gentler software company; at this scale, there's no such thing.