Vantaggi
Mostly good people, they do however, tend to hire people who know nothing about research to be "account managers." Ipsos is a good place to get your market research feet wet. I was happy there for several years under the mentorship of my first manager. I learned a lot and was exposed to many different opportunities and kinds of research. There's a lot of opportunity for lateral moves, if you have a decent manager.
Svantaggi
Overworked and underpaid, required to manage-up in many cases. Upper management tells you they care about your development but, depending on which division you're in, promotion opportunities are scarce. In some parts of the company they only experience promotional or raise opportunities once a year and they have a limited amount of budget to bestow. If you're overlooked for a promotion it's not because you don't deserve one, but because they could only promote so many people and, guaranteed, someone has been waiting much longer than you. As it were, I had to leave the company to get the title and pay I deserved.