Pros
Very smart, driven and talented coworkers. Casual working environment and collegial atmosphere. Flexibility to work from home when needed. Chance to define an emerging industry and answer the application demands of today's hyper connected society. Typical start up amenities of free lunches and snacks.
Cons
Management has been lacking so far. Seeing things improve with the relatively new CEO. Not a great place for work life balance particularly if you have small children. MongoDB has seen a crazy amount of change in the past year. Almost complete turnover of the executive and sales teams. I've worked at several tech startups and the amount of change here even exceeds other places I've worked. Related to that, people seem pretty expendable around here. I've seen some super talented people go without so much of an acknowledgment about them leaving and whether they were let go or left on their own. Hard to monetize open-source software. Puts a lot of unrealistic expectations on sales to solve that conundrum.