Pros
Regardless of how stressful your days are, at least you know you're working towards a good cause. Perks are OK - snack closet, Friday lunches, stock options, etc. Casual office environment - although we're a bit on top of one another due to lack of space, we can wear what we want and be ourselves.
Cons
Remember in high school, how all the cool kids sat together at lunch, gossiped, and generally felt superior to everyone? Well, Opower is one big "cool kids" table. Work-life balance is poor: when you leave to go home at the end of the day, you're still expected to answer emails and requests. If you're not working overtime, people will think you're lazy. In many cases, there is either too little process or too much process. Opower is still somewhat of a startup so hopefully this is a growing pain that will go away with time.