Pros
Great people, great team atmosphere -- at least in the group I was in. I never encountered any real office politics here, just good people trying to do a good job. I would say employee morale was generally very high. RIM is a pretty big company but it didn't really feel like one. This lack of bureaucracy led to greater independence on the part of employees and more real work getting done. Good work/life balance. People were encouraged to do things outside of the office. It was also nice to work with a real Canadian success story. You can't deny RIM makes world-class products, and that's definitely exciting.
Cons
Not always the most challenging/interesting work. Long dev cycles can get dull but that is the nature of the biz.