Pros
Great driven people, fun work atmosphere (if you make it that way) Free reign to take your projects in whichever direction you think is right (be prepared to explain why though). Opportunities are there if you look hard enough, plenty of variety and a huge range of intelligent people to draw from.
Cons
Very little organisation or direction. Constant investment in hair brained schemes means that the current projects suffer staff shortages, small pay rises and miniscule bonus. Management will not let go, there is a need to have a meeting about every little decision, project managers will micro manage your life on a post it note. Be prepared to give at least 2-3 hours extra 3 days a week, the lack of people means you will easily work an extra 65 days a year to make sure you get that promotion (but don't expect a great pay award)