Pros: free food often, flexible work environment
Cons: political, lack of career progression, immaturity
Rackspace attracts very interesting people, so I have found fascinating individuals. And I have worked with all kinds of different professionals, some great, some average.
The culture is very laid back, it is nice to be able to go to work in comfortable clothing, without make up, that is a nice thing. Nonetheless, it can also be very political, even socially immature. There's obvious favoritism, and only a few excel, as it is not based on merit but on relationships.
Some people take it like a cult, some are more relaxed. Landing with a good manager is key for happiness.