Pros
The employees at Ning are passionate about their work and incredibly intelligent. You do not come across incompetence as you would in many other companies. This may be an effect of the company still being small and the managers being able to be picky about who they hire. That said, the people who are chosen to work at Ning are pretty incredible. Employees care about each other, not only in a work related manner. Teams know details about each others lives and keep up with them. Friendships are formed that are fairly unusual for a company. People really care about each other.
Cons
You will work your ass off at Ning. A work/ life balance doesn't really exist. You are expected to work weekends and holidays and will probably not get a make up holiday. You live by your computer and you better love it. Granted, all Ning employees do love it, or else they quit, but if you want a life, family or hobby, Ning might not be the place for you. It takes months to get used to the fact that you are constantly working and don't have a "normal" life. This type of work schedule is just not for everyone.