Pros
Overall I've had a very positive experience at Quantcast. Compared to other companies I've worked for, the people here stand out as being especially smart, kind, and motivated to help the company succeed. Since arriving at QC, I've felt empowered as an individual contributor to notice a problem and take on a project to fix it. Personally, I've observed that taking initiative like this is applauded and generally rewarded. This certainly does not happen 100% of the time but it is much more common than at the two other tech companies I've worked for.
Cons
The main criticism I have is that there can be a lot of disorganization on high level initiatives that seems to stem from poor communication at the mid-manager level. It seems that managers on various teams do not talk to each other enough and there ends up being overlapping work or poor execution due to a misunderstanding of how another team operates. It's frustrating to find yourself in the middle of this and discover some work you were doing is not going to be used because the manager wasn't doing their job. Another strong criticism is that there is no 401k matching at all. I like Quantcast but refusing to provide any 401k matching just isn't classy. As another reviewer pointed out, Quantcast cannot claim to be on par with companies like Facebook and Google without this.