Avantages
MIT is overall a great employer. They offer the stability and benefits that you would expect from such an institution (comprehensive medical insurance, 401k, pension, discounts, etc). I had to take 3 months off for medical leave and MIT's extended sick leave policy meant that I got paid 75% of my regular salary for the entire time. Each department operates pretty independently so depending on where you work you might have very different experiences. My office really values work/life balance. Also, it's hard to beat the name brand of a place like MIT.
Inconvénients
Difficult to move around internally, as departments tend to be their own islands. Pay could be more competitive. The pay ranges are very opaque and it's hard to earn raises.