Pros
Lots of smart, motivated people around. A good group to connect with and learn from. It's a very relaxed atmosphere, but the standards for performance are high. There's isn't a big need for management to exert a lot of top-down pressure because they try hard to only to bring on board genuinely curious and motivated people who work can also work well in teams. Only the self-driven need apply. Office space is cool so that helps with the long hours. Plus there's the bar, the fully stocked break-room with drinks and snacks, a keg, an ice machine, etc.
Cons
Stress. But that's every job. If there wasn't' stress involved there wouldn't be anything challenging about it.