Pros
As with any company, in the right department, there are great friendships and mentors to be found. Schedules are somewhat flexible, office hours are generally 10-6, and unless you're working in corporate there's no formal dress code. Benefits are decent, and you might have the occasional run-in with talent/celebrities.
Cons
With re-orgs and potential mergers happening just about every year, it's hard to feel any sense of job security here at Viacom. And for the most part, all re-orgs have been terribly disorganized with people left wondering who they're reporting to and what's happening for weeks on end. Senior staff operate under a veil of secrecy, and conversations around salaries, raises and promotions can be taboo if not contentious. There's a tendency toward hiring freelancers instead of much-needed staff, and piling more responsibility onto existing staff when employees leave, rather than re-hiring. That said, employees seem to be generally underpaid,e especially if they've remained at the company for a number of years. HR tends to protect the company as opposed to the employees. When a colleague got an outside offer, and went to her supervisor to see if Viacom would counter, she was told "we don't negotiate with terrorists."