Pros
I've worked for 4 startups around this size (51-20 people) and this one is the most mature in terms of infrastructure, process, technology and vision. Everyone seems genuinely united around our vision and values, and the leadership team works very well together. Best of all, it's simply a pleasant place to be because there's a healthy respect for one another and the fact that people have lives outside of the office. I'm enjoying my work more than ever, and I feel this is translating into some of my best results ever.
Cons
Not everyone can afford to work out of urban centers such as San Francisco indefinitely. Although people are able to work from home periodically, there is no policy yet regarding remote employees. At the current growth rate, this needs to be evaluated if we want to hire and retain great people -- especially if we aren't prepared to raise compensation.