Pros
At Joyent you will learn the real meaning of "full stack". The company works on problems that range from low level kernel improvements to API design specifications. This is thanks to the industry they are in, and the brilliant talent you can find across the engineering organization.
Cons
The engineering organization is a flat structure where there are no engineering managers or technical leads. Even though they have implemented some review processes for proposing features and changes, you will have a hard time winning technical arguments if you want your voice heard. Prepare to be shut down by the CTO many times if you're willing to fight for change. There's no culture of empowering people, it's all about being the smartest person in the room. The environment can be really hard to manage if you are shy and non-confrontational person, like many in the company are. This creates a situation where people give up, stop trying and lose motivation to work on new things.