Ventajas
I love working at one of the premier research institutions in the world. I really feel like I'm contributing to the betterment of mankind by working here. The benefits package (including career development like $5K/year for tuition reimbursement) is ridiculously generous. You don't even have to be working on classes that benefit your current job. If you want to change to a career in another field MIT hires in, you can train for that field while you work. Also, the health insurance package is really cheap if you take the MIT health plan option, and your doctors are all on campus (dentists, too). It takes literally 45 minutes out of your day to have a doctor's appointment. In terms of preventative care, I'm in the best shape of my life.
Desventajas
There's a bit of elitism, much like you'd find at any prestigious university. You will run into some faculty who think that anyone without a PhD is a bit useless. On the other hand, you'll also run into a fair number of staffers who seem to have the idea that anyone with a PhD is useless, too. The campus is sprawling and not particularly wheelchair-friendly. The elevators seem to be broken half the time. Additionally, there's still race and gender issues that MIT isn't dealing with successfully. It's still hard for a person of color or a woman to get promoted. This problem is fairly widespread in the industry, society, and Boston in particular, but I feel like MIT could be doing a better job of working on it.