Pros
It's hard to knock a company that has produced and attracted so many successful entrepreneurs. Most of the people who work at MD have been an entrepreneur at some point and many of the people who have moved on did so to launch something cool. Since I have been here, I count seven companies that have been started (and are still going) that began as an idea in the halls of MD. The company even has a financial interest in a few of them. I guess since that's what MD does for its clients; start stuff, it should not be a surprise.
Cons
When you work for and attract entrepreneurs it can be really messy. There are lots of ideas flying around and plenty of changes happening, so if you don't find change energizing, you'll have a tough time at the company. So naturally, the firm has a reputation for attracting and benefiting self-starters and is tough on people that need lots of direction.