Pros
Many say that the people and culture make Rackspace unique and I agree. The motto "work hard play hard" is very true. Rackspace is a very fast paced environment and be careful not to overwork yourself. Remember that a lunch hour exists (I am guilty of that). Other Rackers have told me that they work way more than 8 hour days because they get so involved in what they are doing (because they love it), they loose track of time! Also, if you see something you want to change to make life easier for you, your team, or a customer, you are encouraged to do it! Also, if you are a Mac person, you can use a Mac. If you are a jeans and flip flops person, you can wear that. Rackspace encourages you to be yourself and does not force you to fit into a mold!
Cons
I can't think of anything.