Pros
Get to wear jeans to work everyday, free soda and vitamin water, flexible work schedule (i.e., 9am or 930am start), and no vacation policy. There is a lot of freedom to run with things because it still in a start-up mode. So there is a lot of chaos and need for processes which you can help implement if you have the energy.
Cons
Lack of leadership and guidance on how to get complex projects done and implement processes and systems. There is no professional development at all. They don't pay for continuing professional education credits. Extremely busy environment which prevents taking much vacation so the "no vacation policy" is pointless. Management lacks people skills and don't know how to manage a successful team. There is zero planning so we are putting out fires constantly.