Pros
There are many fun people to work with and many learning opportunities if you're new to the industry. The atmosphere is laid back and great to work in.
Cons
There tend to be limited career paths, and while the talent at Rackspace is good, it tends to fall short in keeping the very best talent. Very talented individuals have left to find greener pastures simply because there isn't the structure at the high end to keep highly skilled IT interested and the "brain drain" is noticeable. Management tends to have difficulty understanding technical subjects and so the praise and rewards tend to be for menial tasks and really solid complex work tends to go unnoticed. There is also a recent push among leadership to put most or all of the skilled IT on-call 24/7 in an environment that already eats into many people's personal lives.