Pros
You are given free room to succeed, and success is noticed and rewarded by direct and senior management. Lots of opportunity for rapid career advancement and development. The company is full of smart, interesting, motivated people. Management has yet to do something that I wouldn't do in their place. The epitome of "doing well by doing good". I turned down a much better paying job when I joined SolarCity, and I made the right decision.
Cons
The company is very de-centralized in terms of employee locations, so there may be a lot of variety in experience. I am not an employee working out of HQ. Many employees are relatively autonomous in the field (for better and worse). This is not a place to coast and requires a large commitment of time and energy. SolarCity decisions can be strict at times, but they're always logical and ultimately fair.