Pros
The perks, food and transportation being the main ones, but there are lots of things that make it a geek's paradise if you're into that sort of thing - games everywhere, free tickets and shuttles for some movies when they open (Transformers was one), etc. Let's face it, it looks good on your resume. The chance to meet some very bright and interesting people. There are so many opportunities to educate yourself about the world through your employer - everything from tech talks on a variety of technical topics to visits by politicians and public figures. It's cool to be on the inside and learn about new products everyone else will be talking about soon.
Cons
My experience was that of an intern so it may not be typical, but I ended up doing work I had absolutely no interest in and didn't envision getting my degree for without much opportunity to do something different. When interns are recruited they don't have much of a say on what type of work they'd like to do, so if you're stuck with something you don't like and want to work on more interesting things, that's what evenings and weekends are for. If you have a PhD you can do some fascinating things at Google, but if you just have an undergrad degree you might be better off at a smaller company where you will get more opportunities to do different kinds of work that span several job positions at Google.
