Vantaggi
Quirky, yes, but I'm convinced that upper management is savvy and knows what it's doing. The work can be challenging and interesting, and fulfilling when you see how it benefits people. It's nice being surrounded by people who are young and smart but not so ambitious as to be too obnoxious.
Svantaggi
Employees sometimes treated like helpless children -- and people rise to the expectations you set for them. People seem to be offered middle management positions on the basis of hours spent at work and a vague sense of project management ability, and certainly not on the basis of their skill or experience managing people. The intent is to have a 'flat' management structure, but in a company of 3000+ the result is a frequently frustrating tangle of poorly supported, unempowered, sub-par middle managers. Not sure if that's any different than any other company, though. The growth of the company has really stretched some of its geek-friendly corporate culture to the limits of absurdity.