Pros
Smart people. Interesting, cutting-edge research. Provides a great bouncing off point for any future job.
Cons
Investigators care more about publishing good results than helping patients get better. "Pubs" are valued more than anything else, and upper management seems to think that they're doing you a favor by paying you minimum wage to do leftover work (that you're overqualified for) with the understanding that they will write you a letter and leverage their connections for graduate school applications. (You don't need them.) Research assistants with bachelors degrees from some of the most prestigious colleges in the country are treated like undergraduate interns. Perhaps this is an issue tied more to the culture of academia than to MGH specifically, but the mandate to be a research machine who isn't allowed to speak in meetings before earning your place in academia is frankly disturbing.