Pros
The School of Medicine has agreed to the NIH mandates of post-doc salaries across the board so you at least get guaranteed that, unlike some other institutions which can take advantage of foreign post-docs especially. It's not like working at a national lab but it's decent. As a post-doctoral fellow or graduate student you actually have GREAT healthcare. The director of University Health has implemented a not-for-profit/break-even self-insurance program that I'm a big fan of. Your healthcare costs are typically covered at 80-100% and your personal monthly premium is covered by your PI*(not necessarily if you're in the school of public health) Unfortunately, your spouse or family monthly premiums will be $250+ so it's best to have the spouse usually on their own employer's insurance. But compared to medical health insurance plans at other high level academic institutions, this is still quite a deal. There's a dedicated UHS clinic just for students and fellows with GOOD doctors and you never pay for any visits there. Also, Dental insurance and vision care are also reasonably good. No benefits for prescription glasses/contacts though. JHU SOM is also great for fostering a lot of collaborative research opportunities that you can seek out on your own or through your PI's connections within the hospital. People are very nice and just interested in the research, not as competitive as you might find at other institutions. You get exposure to amazing cutting edge research too. The hospital gets some of the most if not the most NIH money and there's a reason.
Cons
For post-docs there's no employer matching for the 403b plan so you may as well start up your own IRA. You can get stuck in a post-doc position for up to 5 years and then you can move on to a research faculty position but some have called this a "glorified post-doc" The campus is in the middle of a rough area. There's a reason they are the number one specialists in gun-related wound care. But campus security does their job, just don't be stupid and walk home at midnight.