Pros
This is a fast-paced company. They are growing rapidly, which is a great environment for people who thrive when given opportunities to take on new challenges. I can see where it would be hard for people who prefer a slower paced, more routine job. Enjoyable parts of the job are the people and the sense of accomplishment from helping build something incredible. There is a strong emphasis on work-life balance, with people encouraged to work hard and get their tasks done and then get out of the office to enjoy their personal lives. The group that I work for has a structured program for promotions and advancement. We are evaluated twice a year, and managers work with us to understand our goals, line out what we need to do to advance within the company, and give us the tools/training to get there.
Cons
There has been some turnover of staff, mostly from people who joined the company but weren't able to keep up with what was required of them. People like that tend to blame the company instead of acknowledging that either they didn't have the chops to do the work or that it just wasn't the right fit for them. The people who join the company and succeed are the top tier performers.