Pros
I only left to go back to school and pursue software engineering. If I stayed in IT, I would be at XL for life. Management is awesome! They take the time to listen to you, work with you, advance your career, and help you succeed. Everyone is friendly and will help you. I started on service desk and they built me up to a systems analyst. If I stayed I could have advanced to any position. I learned so much, and made friends for life. Adam, the CEO, is hands down one of the most amazing bosses you will ever have. He takes the time out of his day to hear you. I'm not joking. If you need to talk, he will make time. I've never seen a CEO care so much about his employees before. They provide food all the time, the company parties are so much fun, and the new office space is pretty cool. In short, if you want to learn and grow, while being with the most awesome at bunch of IT folks, work here!
Cons
The only downside was on call when I first started 2 years ago. But management answered our prayers and on call is pretty much eliminated!