There are some great personal account in these answers by contractors who worked for Google. I can give you the interpretation from a full timer.

I guess this hasn't been said on other answers, but I worked directly with Bob See on a good deal of recruiting, particularly during the formation of the Accessibility Team. (Accessibility is in Google's mission statement, but they had no Accessibility team prior to 2006.) I think he did a great job for that team, and we managed to land some rockstars in the industry to get the team off the ground. Accessibility has played a large role in Google App's later success in the education and government markets. I'm glad to hear he felt valued, because he certainly did deliver value.

For consultants and contractors to Engineering team, our contractors were often MORE experienced engineers than the employees. Many were specialists in their field. For example, some teams had Agile coaches brought in from Kent Beck's company, so that we could learn Agile methodology from the horse's mouth. We also had Douglas Schmidt, a prominent expert on Distributed Systems, consulting on protobuf and MapReduce design. I suspect if we needed a course on ethics, Google could bring in the Dalai Lama as a contractor.

Some of the other answers discuss pay. It's an unfortunate reality that Google probably has close to the worst pay inequality of any company in the nation. Even if you ignore the extremes, such as top tier executives vs minimum wage contractors in certain roles, the difference in pay between highly ranked engineers and the non-engineers was remarkable. Factor of 10 pay difference for two people sitting near each other, albeit doing different jobs and with different skills, was not unheard of. @_jeff_nelson