I worked as a contractor at Google X. Working there was great. I enjoyed working with the other engineers very much. Lunch was good. Everyone was accommodating. That said, two things stood out as a problem. Contractors are treated differently in terms of security and processing. It took weeks to get my credentials figured out so I could use email and to use the build system. Security is tight there, and slow. My access to the building took two or more weeks to clear. I was not able to access all of the code I needed to do my job.
The worst part is that contractors are treated as a security risk, so they get no heads up when there services are no longer needed. Just a simple "this is your last day. Clean up your desk, leave your computer, and head out." That's it.
I assume that this technique limits security risk, but from a personal standpoint, it was not fun.