Pros
Well respected name in the industry. Lots of opportunities to expand horizons (if you know where to find them). Certain groups are able to maintain some autonomy in certain respects
Cons
Senior management is laughably detached from what goes on within each of the client-facing business units. But the biggest con about Nielsen is the leveraged buyout the private equity firms conducted several years ago. To pay down the massive amount of debt, salaries were frozen and strong performers are not rewarded appropriately (i.e. low bonuses versus previous years', delayed promotional increases that were half of previous years'). All of these factors have soured people's attitudes, where the people used to be the overwhelming reason people liked their work. The reason there are so many openings is because current employees are fleeing now that the job market has improved. It's only a matter of time before clients start doing the same.
