Pros
WOrking for the Nielsen Company was a mixed experience. While I think the company is certainly headed in the right direction and Dave Calhoun knows what he is doing "One Nielsen" I was not that excited about the actual work I was doing and thus was not that excited about being at the company. However, the company does a great job of keeping all of the employees in the loop about decisions that are made, trends within the company, and future expectations. The company also trys to keep employees happy with small perks (casual dress, free lunch, dinner after 7).
Cons
I don't know if there are any significant downsides to the company, some areas that are not great include the hours which tended to be extremely long. I also am not certain that opportunities outside of the company if you decide to leave are that great because almost everything you learn is very proprietary and thus not very transferrable.