Pros
I've been at MIT for 6 years, with two different organizations, but work very closely with many DLC's (Departments, Labs, and Centers). This place is EXTREMELY decentralized. Each DLC is like it's own little company, with it's own personality, politics, etc. People think of MIT as a place, which it is, but it's far more than that. I think of it like a huge mall. Each store is different with a different vibe or culture. MIT is kind of like that in the way the DLC's are very different. Some have a throw-back 1950's DOD feel, others are very cutting edge working on the latest and greatest things.
There are many many very smart people leading incredible projects and initiatives. It's really cool to be a part of that and interact with so many wonderful people. I've seen a great deal of movement on the administrative (i.e. non-research) end of MIT, so there are opportunities to move around, if interested. The length of employment of many here is simply astounding. I've been here for 6 yrs and still feel like a rookie. MIT is the type of place people never leave. When they do, so often they do whatever they can to get back. I've seen this time and time again...
Cons
Major decisions can be difficult because of the collaborative decision making style at MIT. It sometimes takes FOREVER to get big projects off the ground because so many must have input into the decision making.
Surprisingly, the flexibility here isn't as great as one would think. It's up to the DLC for how flexible they are with people's schedules, but it seems more the norm that this place is "old school" when it comes to working from home or flexible schedules. I think this will hurt going forward as people are so accustomed to having flexibility.
