Pros
1) I've worked on a bunch of different consumer web and mobile applications. Glassdoor is the first one where I've had the experience of strangers thanking me for building a great product that made their lives better. Frequently, I meet new people and tell them that I work here, and they say, "Wow, cool, I use that. That's such a useful {site / app}. It just helped me {negotiate my salary / prepare for an interview / find a new job / avoid taking a job at a company that would have been bad for me / etc.}". 2) It's fast growing and successful, which is exciting. This, combined with the pleasure of building something useful, makes for extremely high morale among the employees. It makes it fun to come to work every day. 3) I commute by bicycle across the Golden Gate Bridge every day to Sausalito. It's a short trip, and it's gorgeous. The office is in a really beautiful spot by the water. There's a really nice deck with a view of the bay and the San Francisco skyline, with a grill and a kegerator full of beer. There's good quality of life working here.
Cons
The down side of fast growth is that we spend a lot of time on hiring and training new employees, which takes time away from "real" work. Also, it's tough trying to get into a rhythm, when we're constantly adding new team members.