Pros
Getting to work on-site at Google headquarters in Mountain View, CA! Free breakfast, lunch, and dinner from dozens of cafeterias on campus. Free access to all fitness facilities. Free food in the micro kitchens. Access to Google shuttles (contractors have to pay $1.50 per ride, though). Hands-on experience with Google technologies such as Stubby, Protocol Buffers, Spanner, Borg, and Piper. Full access to the google3 codebase. Super smart and nice co-workers. SWEs are always happy to review your code. Pay is on par with SWE III (T4) base salaries (of course, I don't get the insanely generous equity package and bonus that they get).
Cons
No paid vacations at all. I actually don't talk to anyone from Vaco that much so sometimes I feel distant. I get self-conscious wearing the red badge while everyone else wear white badges. Also, contractors always get the older equipment. My macbook is a couple of years old and so is my Linux workstation. But at least the workstation has 32GB of RAM. Supposed to be a temporary assignment so I'm gone after a few months :(