Pros
10gen is a remarkably innovative company which hires smart people and listens to interviewees carefully. Everyone you talk to internally goes above and beyond their call of duty to help you, and most particularly, you can ask any question, plead ignorance about any new technology and no one will look down on you. They will instead, teach you what you need to know. They pay very well and the benefits + perks are definitely above average. At 10gen, there is no 'billing' or consulting culture. This is a solid product company. 10gen is also very open about its processes, its code is available to everyone and so are its defect tickets.
Kontras
Some people have a coveted position. They can do no wrong. They can say no wrong. While no one gets fired for standing up, you can be manhandled for saying something the wrong way. A second problem in this company is the cliques. Now it's true that a lot of people get hired somewhere based on their network. Therefore you see new hires coming in from the network of the higher-ups while someone applying off the web site would get far higher scrutiny. The extension of this problem is that, departments are strongly compartmentalized. There is little mobility between departments. To make things worse, every department seems like it's got its place on the totem pole. There are too many 'broadcast' e-mails. Any more than 10 a day is a lot. At 40-50 you're limiting productivity.