Pros
MIT attracts some really talented and enthusiastic people as grad students and post docs. The possibilities for fruitful collaboration and interaction are great, but you have to be savvy about it. (See the cons) Wonderful technical staff. You should really try to make friends with the technical instructors in the shops, academic teaching labs, and shared facilities. There's a lot these people can teach you. Top notch recreational facilities (a couple gyms, a sailing pavilion, all really nice) MIT has a lot of money dumped on it from several different sources. This results in unusual opportunities (like blacksmithing or glass blowing, cool 3D printers, etc) and if you know where to look, you can often rescue useful lab equipment from the trash. Realizing and coming to grips with the cons I've listed provided me an opportunity to cultivate fortitude and wisdom--so not altogether bad.
Cons
Departure from Reality Much of the research is massively overhyped for both its technical audience and the public, often consciously. The differences between what's actually done at MIT and what's done elsewhere are smaller than might be imagined, but the profs here excel at salesmanship above all else. When you talk to people involved in student startups, and drill down to the specifics of what they're doing, you often find they're based on fundamentally flawed concepts. These people aren't being willfully dishonest, they've just succumbed to delusion and it can be heartbreaking to see when you consider the resources at their disposal to figure things out. More Exploitative than Anticipated If you're going to grad school, you basically accept that you're signing yourself into indentured servitude in exchange for apprenticeship. The trouble is that it turns out it's not really apprenticeship at all. Most of the labs here are run like idea farms for the benefit of the career and reputation of your prof, often with little to no meaningful input or guidance from him or her. This can be especially true if your prof has acquired you to do things outside his or her area of expertise. Independence is great, but feeling deeply accountable for the quality of something that someone else is taking credit for can be a tough pill to swallow year after year. Some profs adopt strategies for maximum short term output from their labs that can be pretty brutal on everyone involved (including them). Counterproductive Competition (occasionally) Most people here are great, but there's a small subset that are pathological narcissists skilled exclusively in using others to accomplish their aims, meanwhile reassuring themselves and others of their inherent superiority. This is an unfortunate byproduct of the prestige of the institution--it attracts these types and they can't be easily recognized from a CV or an interview. All I can say is that if you've developed useful capability, you need to be wary that you aren't being manipulated or sabotaged; these things happen. Don't let it prevent you from interacting, but you have to always keep on guard in the back of your mind. This chess game can take some getting used to if you come from healthy, mutually supportive intellectual environments. These people are rewarded and reinforced their behavior before they're spit out into the world.