Pros
A long list of great clients, so whatever team you are in, you will more than likely get experience on a big brand that is top in their sector. The strategy team are some of the most talented people I have ever worked with, and my experience from MediaCom has really paid off in my career, I just wish I hadn't stayed so long and wasted time thinking it would get better.
Cons
As many others have commented, media knowledge in digital is isolated to the digital teams and the rest of the agency have been slow to really embrace digital, although they claim they are multi-media planners. There are A LOT of egos especially in middle to senior management, although the CEO is very inspiring. Pay is terrible and promotions are delayed. Its not uncommon to work long hours and weekends for no recognition. There is not enough experience in the teams, its all grads and management: a workforce of people who either don't know what they are doing or who don't want to do what needs to be done because it's beneath them. MediaCom also have a weird job title system whereby a planner is actually equivalent to senior planner or account manager in other agencies...a media manager is really an account director, or senior account director.. and this goes up to associate directors and group heads, who really should be business directors. Having worked with other agencies in a client-side position, the account manager on my account now would definitely be a planner level at MediaCom. The main problem with MediaCom though, is that they don't charge their clients enough. There isn't enough money coming in to fund the teams to do the work that needs to be done. To that end, brand teams have to constantly up-sell additional services instead of focusing on executing brilliant media plans. Media planning shouldn't be a sales role but it is fast becoming one at MediaCom.