Pros
Hands down, the best part of OpenDNS is the culture. Not only are your colleagues fun and interesting but they're very intelligent and A-players. It's rewarding to work on such a high performing team. Moreover, OpenDNS is full of thought leaders in the security space, which means that we have a very accomplished team solving interesting problems that define the future of security. There's little hierarchy, which means that good ideas shine through no matter who you are, and executives are very accessible. The management structure works very well and managers tend to take the time to give meaningful feedback so that you can develop as an individual.
Cons
As with any startup, the hours are long. However, you see the results of the work you put in, so for me, it's worth it. Compensation is fairly low compared to other tech companies, so you need to proactively negotiate.