This response is a little late for your question, and its been a few years since I've been there but I spent plenty of time at BIDMC and still know around half the faculty. A couple of current faculty were residents when I was there. Its a gigantic dept (there are some 40+ faculty), and one of the biggest pathology residencies in the USA in terms of # of residents. (Used to be #2 or 3, I think; probably still is). Like pretty much every academic place, there is a "core" dept comprised of individuals who have been there many years, and a smaller contingent of rotating junior faculty who are overworked and underpaid, most of whom stay a few years, then move onto something else. About 7-8 years ago they formalized this into an "official" two year junior faculty job, sort of like a super-fellow. Like every dept, it has its share of internal politics and problems, most of which won't really concern you as a resident there.
In AP, dept isn't really weak in anything, but exceptionally strong in breast and GI pathology. You'll get more derm exposure there than the other Harvard places. No dept is perfect, but faculty there is far nicer than many other places, and general hospital environment is nicer. Tagline of "Harvard with a heart" is generally true; its a good place to work and to be a patient. Hospital itself is cutting edge, with excellent IT system. OTHER depts are generally excellent. On its own BIDMC is a world-class institution, but of course being physically smaller and less specialized, its always overshadowed by the other big two Harvard teaching hospitals (both of which, also, by the way have excellent pathology residency programs, though of completely different character and emphasis than BIDMCs).
Unlike some pathology residencies that will take any warm body as a resident, BIDMC can be choosy about whom it accepts, and so it is. But residency program itself is highly structured and committed to turning out good residents. CP training there has traditionally been strong, especially blood banking. Unlike many places, the CP residents have a formal curriculum and actual responsibilities, and get real training (ie its not, "here' the book, there's the lab, see you in four weeks"). When I was there every married female PGY2 resident got pregnant (by design. . .it was the best time during residency to have a baby). I understand they have a new residency program director, he's a CP guy, so I doubt this has gotten short-shrift.
Residents work hard, but aren't completed scutted like at some places. Its a high workload, high training, complex case environment. Emphasis (unlike MGH and Brigham across the street) is more on turning out strong community pathologists, rather than researchers, or high-depth/low-breath "experts", though plenty do stay in academia from BIDMC. Path residency itself has a good reputation for putting out high quality graduates, particularly in New England and Northeastern USA. That's a plus later when you're looking for a (hard to find) job. There are half a dozen or so path fellowships associated with institution. . .internal candidates generally get preference. You may want to do a subspecialty, you may not, but at least having the option is a big plus. Some of these are prestigious.
In terms of change, what changes are you talking about? Of the 40 faculty, at least half of them have been there for over a decade, and many quite a bit longer than that. There is a new residency program director, but there is also quite a bit of institutional memory and inertia. . .they're always talking about coming changes that don't happen.
Boston, of course, is a great city in which to live as a young adult, and a great place to train in medicine. Some say its the "Mecca" of pathology. There is some room for interaction with other pathology departments (eg New England Path society mtgs are big). But its also expensive to live there, and your resident salary won't go far. If you have a family to support, its going to be a lot harder to make ends meet there than some other places.
Bottom line, if you're a single person, and you're interested in community pathology after graduation, this is (IMO) a no-brainer. If you like the place, go there. You will NOT regret it later (I didn't). Only reasons NOT to go there are a. If you have some geographic reason for not wanting to be in Boston, b. You've got mouths to feed and need a lower cost-of-living place to help make ends meet c. You are an MD/PhD and are dead set on a research/academic career. *IF* c, BIDMC is still OK, but there are other places more attuned that that career track (eg Brigham, Stanford, etc), and you may be better served going to one.
