It really helps if you can get in the Racker Referral program, that way your chances of getting noticed are much higher. My process started with a phone interview with a recruiter which was about a week after I applied. The questions were pretty basic, some personality and some basic tech questions like "name some default port numbers" (HTTP, DNS, SMTP, MYSQL), familiar with LAMP stack? etc. They really want to make sure you fit the core values at Rackspace.
After that I was set up with an interview the next week. Everyone's experience will be different so be warned. I was interviewed by 2 groups of people, each took about an hour. It was about 70% personality and 30% tech questions that I listed on my resume. They are really trying to find out if you would fit in with them. You really have to be yourself! Mix in interesting things about you (hobbies) and any skills you know when it's applicable. Do not B/S anything and be really transparent about yourself. Try and do some research on who is interviewing you and what they're into to have an upper hand. All in all it was a fun experience and I can see why people would get intimidated. They gave me a tour of the castle afterwards. Good Luck!