Pros
It's a start up, so you get to have your hands in a lot of different projects and activities that you wouldn't necessarily be exposed to at a larger company. You can learn a lot in that respect and it's a good resume builder. Most of the people are nice and good to work with. I was paid well.
Cons
The CEO has no business leading the business. He's a very smart individual, who excels in academia and engineering, but he has no clue how to successfully run and scale a business. He needs to step down as CEO and bring in someone more experienced in that area if he wants any chance of the company being successful. He's a terrible people manager who gives no feedback and doesn't set clear expectations. (at least on the non-engineering side of things) The Chief Sales Officer is extremely difficult to work with and everyone has problems with him. The CEO gives him too much deference and influence. His sales team consistently underperforms, yet it's the individual sales people that get fired instead of him. It's time for him to go. In general, though they promote a culture of lifelong learning, they don't set anyone up to succeed and don't give you the change to actually learn and grow in your role. They just fire people left and right. I've never seen such a high percentage of a workforce fired in my life.